is it true that when you have sex for the first time, your breasts will grow?

does implantation bleeding usually last 6 days?

No, your boobs don't grow! Who told you that? I wish! A penis doesn't do anything to your hormones except make you horny! You need increased progesterone and estrogen to make bigger ones. That's why women on the pill often get bigger breasts. Mostly from the synthetic progesterone called progestin, though. And, no, implantation bleeding is just spotting which can be a definite cue you are pregnant and supposed to be having your period.