D.B.
He's not getting quality sleep - not at night, not at naptime. He's waking up and can't calm himself down to go back into REM sleep. You have to stop nursing him - or feeding him at all - at night. He's 16 months old and he does not need to eat at night - ask your pediatrician or lactation consultant or anyone with knowledge of children's nutrition. He's hanging on to you - literally, by the breast, and figuratively, by the crying. You must brak that cycle - he absolutely needs good sleep for brain development, so you must go through some short term torture for the long term good.
Research Ferber and sleep training. It usually takes 3 days for a child 6-12 months. Yours might take longer since he has longer habits. Have someone else deal with him at night so nursing is not an option. There's a 3-day weekend coming up - our pediatrician told us to use that as a do-or-die time to be miserable but get him to calm himself down and self-soothe. If he learns you aren't coming back in and he's not nursing, he'll give up. You'll learn how to go in at 15 minutes, then 25, then 35....no picking up, no feeding, just a little back pat and a few soothing words. "It's night time, time for sleep, see you in the morning" or whatever you choose. Be sure Dad is on the same page and uses exactly - EXACTLY - the same words. Same with Grandma or anyone else who helps out. No caving in.
It will be hell for a few days and then you will be done.
As it is, he has disrupted sleep and he's a mess. You must change this. I know it's awful but you will be happy, and so will he, when it's done.