Great board!

I'm a new to lifting so please bear with me if this is a dumb question.

I've been lifting for about 2 months. In that time, I've experienced alot of DOMS. I like that kind of soreness, I think of it as positive feedback.

However, there's another very different pain I've had lately in my left arm. The pain is sharp and only presents itself when there is a load on the tri/bi muscles. It started in the tricep and now seems to be in my bicep as well. What happens is, when I put a load on the tricep, such as when doing dips or bench presses, it feels like a knife is stabbing my tricep, and then the muscle loses all strength, like it just shuts down involuntarily.

The tricep pain started after a day when I put too much weight on the bar and did incline benches. After a couple days, the pain seemed to go away. But as soon as I do something heavy again, it comes right back and I have to stop.

The bicep pain started after I arm wrestled a friend who was stronger, we were testing my progress.

Now it's gotten to the point where the pain is almost always there. I've stopped all lifting until I can figure out what this is, or until it goes away completely.

My question is, how can tell if this is a serious injury like a tendon strain or something different like a muscle tear? Should I just rest it for awhile or is it imperitive to see a doctor? I'm thinking a doctor will just tell me to rest it and not really get to the root of the problem.

How will I know when it's safe to use it again. So far, everytime I think it's healed and I go back to lifting, it starts hurting again. (The longest I've rested it had been about 3 days)

Thanks!

PS: If it makes a difference, I'm a 37 year old male, healthy but not muscular. (I want to change that if it's not too late in life already) 5'8" @ 150lbs and 16% BF. Not taking any anabolics.