Why are my breasts sore?

I’ve been taking my pill for a little over 4 months now and now I’m starting to get sore breasts and gaining a little weight which is weird bc I’ve been trying to diet. I did have unprotected sex about a month and missed my pill that day so took a plan b. Little did I know I didn’t need to but I was just trying to be safe. But now my period comes about every other week and a half and it’s been a while since I took the plan b to regulate my period back to normal, but now I’m have sore breasts and I’m gaining a little weight I think; I took a test and it was negative. Either I’m going crazy or something but has anyone ever had side effects of the pill a while after starting it? I’m just worried