S.H.
Well, I used this book as well. It really helped with my firstborn. It is a reference to "help" get ideas and solutions. But like anything "adapt" it for your baby. Yes, your baby is only 3 months old.. still "new" and needs to be fed on demand etc. They need nourishment when they need it.
He's still young... give it time.
But, at 3 months old, a baby also goes through growth spurts (ie: they get hungrier more often and need to feed more often) and they also go through growth changes and cognitive changes as well. THIS does interrupt their usual pattern of sleep. So bear that in mind. But it will return to more regularity. It's a phase. But you need to adjust to that too. For example, when my babies went through changes like that, I DID get up during the night and addressed what they needed and/or fed them too. I never with-held a feeding or withheld picking them up in the middle of the night if that is what they needed.
Infants go through lots of changes...but consistency helps. They are growing and changing so much each month, and every week...no sleep pattern will be absolutely static.
A "schedule" does not have to be "strict." It's mainly important to have a routine. But if you keep to a "routine" and consistency....it DOES help in the long run. I learned that with both of my children. Think long term. So anything or any routine you start now... will contribute to long term ease of putting them to sleep/nap, later.
A "schedule" to me, means... having regularity in pre-sleep/nap routines... and the time you put them down. And there will be times when it has to be adjusted.
For me for example: my baby wakes, I give him his milk, play or awake time, then give him his milk, go to nap. There is a window of about 2-3 hours in between, of "awake" time, before they get tired again. My boy, wakes up about 6:30 in the morning, and then naps at 9:30 (he naps for 2 hours), then he naps again in the afternoon at 2:30 (he naps for 2 hours). 2 naps total. Then at night he goes to bed at 8:00-8:30. He still does this even though he is now 20 months old. He is now so used to his "routine" that he does not protest when he goes to nap or sleep, and sometimes he will even "tell" me when it's nap/sleep time and will start going about his routine. He will take my hand and take me downstairs, get his stuffed cow he sleeps with, lies down on the living room pillows (this is where I then read to him for about 10 minutes or let him watch his favorite "Little Bear" DVD),give him his milk, and then I change his diaper, and then pick him up, go into the bedroom, make the room dark, put on a fan on low, sing him the same 2 songs while holding him, put him down in his crib while still awake, then put up the railing, walk out of the room, and close the door. Done. This is just my routine, and it works so well with my son. BUT IT HAS EVOLVED OVER TIME. It's not perfect from the start... it evolves. You have to see what works and what doesn't. But, with each "new" thing you try, give it time. A lot of it is also trial and error.
But again, his sleep patterns went through bumps in the road too... at developmental changes, and so we just adapt through it.
But yes, it takes time. Each baby is different. Just keep trying with a routine that works for you both. But a baby WILL get used to a routine... they will begin to "know" what to expect and what is going to happen next. My firstborn on the other hand, was much more spirited, so it took time in getting her into a routine. But as she got older, and I kept regular about it... she "settled" into it.
If he's starting to wake more at night...maybe he is hungry. And if he is hungry, feed him. He is growing and changing. 3 months old is a time when this happens. It will pass. A baby will go through lots of sleep pattern changes... it is not static..but you can get them to be more regular...while addressing their needs. For myself, I don't believe in with-holding feedings just to get them "used to it, in order to sleep longer" kind of thing.
See what works for you. I know it's not always easy. Perhaps your baby is just wanting to spend more time with you after you get home from work, and so he isn't settling down so quickly at bed time? Perhaps, he is having a growth spurt and is hungry and needs to feed more? Sometimes too, if they are "over-tired" it is actually harder for them to fall asleep. Does he nap during the day?
All the best,
~Susan