Chest pain, what is it?

it is on the right side of my chest, and it feels like it is on the ribcage almolst. it hurts when i inhale really deep, and like only for the last second of when i inhale, then the pain is gone when i exhale. it also hurts if i press on it. it feels like the same pain you get when you press down hard on a bruise. if it matters at all, the pain started about 15 minutes after i was at the gym, and i worked pretty hard that day. this is 24 hours later and the pain is still there.