Strange recent prolonged shoulder issue

[Biggerp73]

I injured my left bicep about 18 months ago during the negative portion of a bench press. I could train it without problems except in certain movements it would hurt a bit. Then I tried going heavy on the seated single arm cable curl a few weeks ago, and it's been really hurting since then. For example, today during dumbbell side laterals, it was giving me a lot of pain. It's the outer side of the bicep right where it attaches into the elbow.