I'm 19 and healthy with no allergies. I woke up this morning with a cluster of small mosquito bite like bumps underneath my left breast? Any ideas?

? a reaction to the bra, a bed bug bite, or less likely a fungal infection, if it is scaly / itchy, few other possibilities are there, can't give you a definitive answer without at least a picture, can apply anti-itch cream OTC, if it improves fine, if different you need to see your doctor.