weight lifting soreness not healing?

I've been lifting weights on and off the past 20 years. I know what it's like to have normal muscle soreness.

But recently, I noticed some muscles stay sore for many days after I lifted weights, and I'm not even lifting much (just 10 reps, 1 set).

For example, I might do some curls. The next day, my biceps feel fine, but some muscle near my thumb and some muscle near the elbow starts to feel sore. They are not constant soreness -- I cannot press on a spot and feel the soreness, rather, I have to be moving my arms/hand around to feel the sore/ache.

Another time, after doing some legs extensions, my entire right leg, not just the quads, started to feel sore/numb (as if I slept on the leg) for a few days after that.

Anyway, is there any guess as to what the cause may be or how to go about figuring out what's wrong?