What’s happening to my boobs??

I’ve recently started doing stuff in bed with a boy I’m seeing, I haven’t done any of this before but we haven’t had sex so that isn’t the answer

I’ve come back from his today and my boobs are so painful underneath and on the sides

I’m not due on my period for another 12 days, either it’s going to come early or something else is happening???

Anyone know what’s gojng on😂