Tender breasts?

Clare
So lately my breasts have been really tender, especially today, 5 days after I had a very short period. I have the nexplanon implant. Over a week ago I ended my round of antibiotics and steroids which I know messed with my birth control. Basically in the confusion this month I have taken every precaution to not get pregnant; 
condoms, plan B when one leaked, and A LOT of drug research.
Is it even really possible that I'm pregnant? 
I'd think I'm probably not but why have my breasts been so tender and swollen over the last couple weeks?