Sleep regression! HELP!

Garrett • Dual military couple 🇺🇸 3 boys 💙💙💙

So my son was sleeping so great. From about 5 weeks until about a week ago (he’s 3 1/2 months now) He used to sleep 7 hours straight.... now he’s up every 90 minutes. He started to get really sleepy about an hour and a half before his normal bed time, I kept him awake for about an hour before I couldn’t take feeling like a monster any more. Would keeping him awake even make a difference? Or am I just torturing my poor boy by not letting him sleep when he wants to. To top it all off my husband is away for work and will be for another 3 weeks or so. So I’m all on my own and having to go to work everyday myself. I’m beyond exhausted and would love any tips you guys have to getting him to sleep just a little bit more. I’m at my wits end.