Its a period. I get mood swings every three-four weeks, including bloating and intestinal issues like other women in my family get. Just no bleeding, obviously.
I'm pretty sure uptake of the estrogen, even if its off schedule from your shots, is done in a periodic way. Progesterone IMO makes it worse, if its affecting you badly, stop progesterone. It'll still continue with estrogen but it won't be as pitched.
A lot of TERFs act like this isn't a thing, and there isn't a whole lot of data on it. But I've talked to enough trans people that I can say its a common enough experience.