I've watched a few videos discussing how cramps happen and it seems to mostly be nerve stuff going wrong, being dehydrated and muscle fatigue. However, I'm able to easily give myself pains very much like when I get leg cramps simply by flexing/stretching my leg in a specific way. I also often get cramps when I try to make my foot form a straight line with my leg using muscles in my lower thigh where the cramps happen, and it sometimes happens when I do it for swimming

I've also often had cramps in the past, sometimes while sleeping, often when I do even slightly intensive exercise like running a round or 2 around a school

Can someone explain in laymen's terms why I easily get cramps (or cramp-like pain) when I stretch my leg muscles certain in ways?

@ChocolateOverflow There are stretch receptors in your muscles/tendons that tell your brain how your body is positioned and help coordinate movements. They also protect you from injury, to make it hard to, say, break your own elbow by trying to lift something too heavy. If you push a joint too far one way, there will be a signal sent in your spinal cord to contract a muscle to counteract that stretch

It's possible you're stretching wrong or overdoing it, which a physical trainer might be able to help you with. Otherwise it's possible there's something medically wrong and you should see a doctor.