it happens to me. I am not sure if it is from the hitting of the balls from beating off or from the balls getting overworked

I once read somewhere that if you have really intense sessions that it can happen, it's due to increased blood flow to the area and muscle spasms? Not sure if that's true or not but doesn't seem to be a cause for concern cos anytime it's happened to me, its gone away quickly enough and isn't enough to be super painful or concerning.

it can happen sometimes, usually from you balls bouncing around

Things can get sore down there, but it’s more of a persistent aching or dull pain, not something acute. If the latter it might be cause for concern, but otherwise it’s just your body’s way of telling you to cool it. Lol.

My testicles have gotten sore in the past when I masturbated a lot in a single day, but it never lasted very long

I am not sure I believe the "balls having to work harder" idea because, AFAIK, they produce sperm continuously at the same rate whether you ejaculate frequently, ejaculate less often or even never ejaculate.

There are a couple of other possibilities. One is what is often called "blue balls". Obviously they don't literally turn blue, I think it is blue as in singing the blues etc. That is usually more of a dull ache than a sharp pain and people more usually have that when they have been highly aroused for a long time without cumming, for example making out that goes on for a while but never goes any further. This is caused because the arousal causes increased blood flow to the whole area. It resolves once the arousal has come to an end so usually that will happen faster if you cum, so on getting home from that long make out session it can help to masturbate, but will also resolve on its own if your mind turns to more mundane things for a while.

If that is the explanation here then maybe the issue is that something has caused you to spend most of the day aroused and that is what caused the frequent masturbation rather than the masturbation being directly responsible for the ache.

The other is just banging them around too much. If that is the explanation then maybe work out how to make them move less.