I have been getting sharp pain under my left breast(ribcage) for months now. sometimes hurts when taking deep breaths. heart related?

Unlikely: These kind of sensations are not rare. Very frequent actually. That said, you do need to get into the habit of doing self-breast exams. Same time every month, either in shower or lying down 2-4 days after your period ends. "lawn mower" technique advised. W/respect to cardiac worries, need an in-person eval to listen to heart sounds, get chest XR & 12-lead ECG, which may prompt echo & telemetry.