Are you comfortable with bed sharing? That might help. I did it with DS1 out of desperation for a couple of months even though it was one of those things I said I would never do.
If you think it's related to teething, you might want to give him some Tylenol.
Letting him sleep on his belly might help as well when he learns how to roll over from back to stomach. Good luck, I know it's really hard.
Welcome to the 4 month sleep regression. There isn't a lot you can do. We bedshared so I could just nurse him without getting up. It's brutal to be travelling at the same time - sorry. Good luck.
Ditto the others about the 4 month wakeful. I know it isn't really helpful but we went through the exact same thing. It was really bad for about a week, and then kind of bad for about 2 or 3 weeks, and then he settled back down and now wakes up once or twice a night, nurses, and goes right back down.
Ditto bed sharing. It helped me get a lot more sleep because I don't really have to wake up. Unfortunately new skills and developmental stages often lead to less sleep and their little brains seem to go on hyper drive around that age.
It also seemed like he was able to feed better at night because there were fewer distractions so he made up for lost time. If I made an effort to feed him in a dark quiet room during the day, he slept somewhat longer stretches at night (like 2hrs)
For us the worst of it lasted 3 weeks, but my almost 7 month old still doesn't sleep through the night like he used to. We get maybe 2 x 4hr stretches during a week. I drink so much coffee now