Bicep pain

I’ve been feeling bicep pain in the belly of the bicep. I have 2 very small bruises in different spots of the belly if the bicep. It’s fine when I’m playing catch but when I long toss and pitch off a mound, it feels like it’s being pulled. It’s been hurting for 3 days now, since my last mound visit. Any idea what it could be and what might be causing it? I have had a problem of over striding and over extending my torso when I pitch. Could
That be it? There is a showcase coming up in 2 weeks and I want to be 100%

Get an MRI. My 13 year old son was having bicep pain while throwing. He has a partial tear of his MCL .