Tender/sore boobs

Ok so my last period was 1/5-1/7. I typically get breast tenderness/soreness about a week before my cycle and they last up until a few days past my period. I didn't feel them before my period, only after and its stuck around! 😭 its been like 3wks or so and my boobs are killing me!! What causes this? My breasts feel so heavy and sore/tender, its uncomfortable! This was my best friend's first pregnancy symptom so yes I've take a few tests at random just to rule it out and they're negative. I'm not on birth control or any meds other than vitamins. What could it be?