Hi sweetie, welcome
I'll try to keep the abbreviations out, but let me know if I slip
There are a few things that could be causing your issues:
1. Growth spurt - there's a massive one around 4 months that can last around a week and does involve more night feeds just because baby is growing heaps.
2. Developmental change to sleep patterns - sleep becomes more cyclical and baby goes into lighter sleep and has to learn to make it back to deeper sleep.
3. Discomfort - reflux can flare with teething (get worse) and teething itself can cause sleep disruption. I'm not sure what tylenol is - paracetamol or ibuprofen, but ibuprofen tends to work better with teething. Reflux also tends to get worse around 4 months, so maybe its time to look at controlling it medically. You could have a chat to the lovely ladies over here:
http://babywhispererforums.com/index.php?board=13.0 about natural ways to keep baby more comfortable too.
4. Day routine leaving him overtired by the end of the day - I think either his naps are short developmentally or because of discomfort - refluxers often have short naps because when they go through the light sleep cycle, they wake and cannot get back to sleep due to the discomfort. How do you go extending his naps? At this age, he should have at least the first awake time up around 1hr50-2hr - that may help with the nap situation or may at least give you an overtired nap that you can resettle more easily so he can get a good restorative nap in first up in the morning - can make the world of difference to the rest of the day in most cases.
He sleeps swaddled, but has recently been breaking out of it & cries when I start wrapping him up. I think he doesn't like feeling constrained, but he can't sleep without being wrapped up.
He may be telling you he's not ready to sleep yet - as in he's undertired... he may also be ready to wean the swaddle - you could try one arm out first rather than going cold turkey.
Now he's starting to teethe, but even if I give him tylenol before bed, he still wakes up every 2-3 hours (sometimes every hour).
This is classic waking due to pain. I really think that you need to take him to the doctor and talk about options for controlling the reflux - no baby is going to sleep while in pain.