Hey there!
So, I have bicep tendinitis- I’m pretty sure lifting my school bag for university many times a day aggravated it. I know the pain you’re talking about!
It REALLY sounds like you need to rest that arm, get some ice on it, and perhaps see a doctor.
If you overwork the muscles, you run the risk of damaging or tearing something. For me, it tends to be tendons, but for others I’ve heard of major muscle tears and even worse.
The pain you’re talking about after shoulder-mounting so many times is a huge warning sign to STOP and to rest! Your body has limits and is not a machine! Pushing too hard, too often, or very repeatedly can seriously damage you.
My suggestion would be rest (as in, no more shoulder mounts, and very, very little use of that bicep at all for some time, weeks at least), put some ice on it each night where the pain is, and possibly see a doctor to make sure there isn’t more permanent or difficult-to-treat injury.