Bra issue... Tight at the side... I'm in pain so please help ?

So I'm a bra size 36B and I'm still 15 and I've been uncomfortable lately. My bra's been bothering me. Well after I remove my bra it hurts quite a lot and there are marks at the side... The rib part's okay... Does this mean my cup size is increasing or does it mean my bust size's increasing... The band size is the same...