That kind of pain is often small muscles around joints and ligament anchors - this has happened to me a couple of times in different places, just doing the same stuff that 20 years ago wouldn't have caused the slightest problem. It happens when your mind doesn't realize you've pushed your body past what it is presently capable of.
Essentially, it's muscles that have been overworked, which causes them to fray, then they start knotting up as a preservation and defense response - not in a charlie-horse kind of way, but in a scar tissue kind of way. It's made worse as, often, we go to bed exhausted from whatever that overwork was (ie, breaking down an animal, moving house, etc), and they kind of set like that overnight, "healing" in that improper knotted state. If they get broken down hard enough with overwork or trauma, they stay screwed up and knotted, easily agitated, and easily re-injured.
Muscles are a bit like rope, with grain structure, right? Knots are essentially that structure fraying, then healing all balled up. Only way to fix them is to break them down and stretch them out to a more linear state, let them heal with regular massage and stretching until they get back to normal. The heavy and intense massage breaks them down, the stretching gets the grain structure better aligned. It takes both intensity and consistency. Sometimes it takes a percussion massager or a hard implement, and the break-down part can be painful as hell. But it's a unique pain, that's not the same as grinding on healthy muscle. The difference is obvious and notable, when you hit the right spot/knot, etc. In complex structures like hands, it can be multiple sets of tiny muscle systems layered on top of each other, where you need to get through one layer of damage to start getting to the next one. But learning how to find and get to those damaged spots can take a little learning, especially in the hands and deep in the forearm or shoulder.
Focus on doing the break-down and stretching in the morning, and stretch with light massage throughout the day and before bed. But do not do the break-down part in the evening, or it will tend to knot up again overnight with it not being used.
