Four sons? You are an amazing mother! I read your message and it took me back to a really unhappy place, but now I can laugh at some of the things we endured, so be encouraged. My son trained me to be his mother. He is our firstborn, and he didn't fit any baby model I had ever witnessed or read about. He'd take power naps (20 minute increments), wake and cry. Stay awake for hours, only to start the cycle again. I'd call friends (most who had Gerber babies who just cooed and smiled), who'd ask me, "Did you feed him?" Duh! "Did you burp him?" Of course! "Did you change him?" Etc. Nothing worked. I remained exhausted, cranky, and sad to see my baby so miserable. I started doing things like putting him in bed with me while hubby was at work, out of desperation, when I realized he'd sleep a little longer in my arms. Before I got too sleepy, I'd try to move him to his crib, and--yep, he'd awake and cry as soon as he hit the bed. Eventually, I'd join him. LOL! Yes, he was lactose intolerant, but the crying didn't stop even when switched to soy or rice milk, which was only a few days after he was born. I look at his baby pictures, and there are quite a few where he has this blank look on his face.
DIET: I don't know if it's the same with your baby, but frankly, I think my baby had either a leaky gut/weak digestive system or reaction to the sugars in the formula. He is now 11 yrs. old and still takes a long time to have a BM. He eats vegetables, more than my daughter, and drinks more water. He gets migraines if he doesn't have enough water or too much stimulation or certain drinks like Kool-Aid or Countrytime, which have a lot of sugar. We now allow only Turkey Hill lemonade or Capri Suns. Drs. say he's healthy and are not concerned about the constipation. He's been diagnosed with asthma, ADD, had chronic ear infections until he was 6 and we began homeschooling. The more I read about LDs, I see relationship between these illnesses and toxic systems caused by undiagnosed parasites, excess yeast (sugars), poor digestion, etc. I haven't taken him to a naturalist, yet, and his Dr.s' won't really speak on natural/holistic remedies or testing for parasites. But, I'm still doing my research on IBS, H pylori, colitis (which I had years ago) and immune system functions. (He very well could have inherited these problems from both sides of his family.) Of course, I'm not urging you to seek out these things, because your baby is too young; it's just something to watch and monitor over time. I'm trying to understand our reaction to sugar, which can be found in formula, so read the your label. Not sure if you're breastfeeding and supplementing. I was unable to do so, though I received quite a bit of pressure to continue trying. My son as a baby wasn't getting enough food from me, so we had to go with formula. Do not experiment with your baby's nutrition, though. I do not have any evidence on any of the information I shared with you and would not want to mislead you on either a diagnosis nor treatment. Take this time to read and watch, only.
STIMULI: There are other things that could be affecting your baby. He could be overstimulated with three older brothers in the house, or very sensitive to some of the household noises you all take for granted. Some things that did help when my son was a baby included holding him close, singing to him, or reading to him (google "sensory integration). It was heartbreaking, and honestly it was a factor in my choosing to go back to work instead of staying home with him when he was a baby. Had I known then, what I know now, I probably would have tried a little harder to connect with him and help him adjust to life on the outside (of the womb). Eventually, with the birth of my daughter, we chose to homeschool him, and he's now a well-adjusted, outgoing, young man. Pros, he eats small meals more often, he gets more water throughout day, and gets a little more sleep. He still has trouble getting and staying asleep, which I believe are connected to the ADD, and make me wonder if he was showing me as a baby who he would be. My daughter never went to daycare, though, and my mom taught me how to properly swaddle her (great book on sensory integration issues: The Out of Sync Child by Carol Kranowicz is in the library). I was able to keep things calm while she slept and kept her near me while teaching my son throughout the day. (Mom and I both worked when my son was born. I quit before daughter was born.) Daughter was a happy baby by comparison and had fewer adjustment problems.
CONCLUSION: Just be encouraged. I used to feel like I was a part of some evil experiment on the effects of sleep deprivation. LOl. I learned that I really could survive on 4 hrs. of sleep for several years! Honestly, if there really is nothing physically wrong with your baby, know that you, too, can survive--and so will he. We're in our 12th year of parenting, and I have only a few abnormal ticks and moments of insanity. LOL.