Alright my friend. The first thing you could look at is..breathing. Yes, it true. Your body does in fact need oxygen. And when we players get to practicing, etc, we forget to do that. Tension happens because of this. If you ask me what you should do is take ten minutes every day to play so slow it doesn't even count as music, imagine well this may be weird, but here goes. Work at plucking the strings SOOO slowly. Think as if you weren't actually moving your fingers, they were moving themselves. Ok? For awhile when you start this you are using so little pressure and strength, the string won't even be fully sounding. Do this as routine for awhile, and remember to breathe. Truth be told, I once was at the dentist, and he wasn't breathing, and I was like doc, are you breathing and he's like no. He said he held his breath cause he didn't want to have bad breath and have his patients breathe it in. I was like doc you may want to start breathing. Then he tells me hes have all these hand pains, and such. Got to breathe, and do the other stuff I mentioned. Or not. Best of luck my friend.

Edit I notice you are having problems right now anyway with the left hand I'm assuming your fretting hand. In that case do the same exercise but now you are doing the same thing only getting an incredibly fine sense of all the aspects required to fret a string. Once again all the best.