Advice PLEASE!!

My son turned 4 months yesterday.... For the first 2-3 months he slept pretty good, woke maybe once a night, I would swaddle him up snug and he did great.... But now, all he does is fidget and roll and grunt and fuss all night long, once he starts that fidgeting that's it he wakes himself up and will not go back to sleep, sometimes I can pat/rub his back and he will go back to sleep sometimes I have to give him a bottle.... I am a believer in letting him cry it out, but I also have a 5 year old that I'm trying to not wake up, and it does not usually work anyways.... I have no idea how to break this cycle. What can I do to make this fidgeting stop, so he, and I can sleep better..... ?