Left Arm Pain When Pressing/Benching

Been running 531 for a few months now and I’ve developed a pain in my upper left arm that hurts whenever I press or bench. It’s painful even when lifting the bar but seems to improve when I get to the heavy sets. The problem is this injury is not improving even when trying to work through it. I’ve taken time off and it does nothing to help. I’m at the point now where I have no idea how to approach this because I cannot carry on the way I’m going.

I know it’s hard for people on here to know exactly what’s wrong but has anybody had any similar injuries and is there any lifts that are good for rehabbing such an injury? It’s hard to pin point exactly where the pain is coming from but it’s somewhere in the upper arm, possibly in the delts.

I should probably mention that I’ve been benching and pressing for years on programs like starting strength and madcows and not had any issues. This is definitely not a form issue.