Period after Egg Retrieval

I just had my egg retrieval on Friday - I had a little bit of brown spotting right after, that stopped on Saturday. Well tonight I started to get what looks like my period. Its not a full on flow, but there was quite a bit of bright red blood with some bits of tissue in the toilet (sorry if TMI) - which usually happens to me when I start my period. It's only been 4 days! I'm scared something more serious might be going on - I've never heard of anyone getting their period this quick after an egg retrieval. Side note - my boobs stopped hurting tonight as well (which also usually happens to be right when I start my period).  I should also mention that I did a lupron trigger - I was reading something that said that could can affect your cycle length, but I'm not sure if that's true. Any insight would be appreciated! It's just way quicker than I thought. We are doing a FET and I wasn't expected to start then next phase so soon.