I am unable to fall back asleep after MOTN feed

Baby is 4 months old and is sleeping well (fingers crossed). He wakes up once around 2-4am for a feed. He’ll take the 8oz and fall back asleep. Me however, I can’t. I have been staying up all morning until I am up for the day. I’ve tried not using my phone during the MOTN feed, no tv on, in the dark, and even with my eyes closed lol. I Just lay back in my bed tossing and turning in the dark.

I don’t know what to do. Anyone else deal with this and what can I do? This only recently started happening. Only things that’s changed is I’ve been dieting and exercising.

Edit: thank you everyone, I didn’t realize this was a common issue!