Generally, pain is not a symptom of MG, but the things you describe could be due to muscle weakness from MG. When all the cells in your mucles aren't functioning (due to MG or other issue), the ones that still are working get overworked and can cause pain.

I have had similar problems on occasion. When I first started getting MG symptoms, I had weakness in some muscles and actual muscle cramps in other places, it felt like I had a knot in my muscle that was extremely painful. I don't get those painful symptoms anymore. If I remember right, I often had the left side of my body get weak and the right side go stiff with tight muscles. MG does not effect everyone the same, nor does it effect any one the same all the time.

I do get achy on occasion if I sit in my chair for too long, or do any one activity for more than a short time, and I do get a lot of popping in my joints when I am weak.

If I type for too long, some of my fingers get tired, others go stiff (my pinky finger loves getting stuck in a straight position), and I often get twiches and click things with my mouse that I didn't mean to.

I don't exercise much these days but I'd love to. My exercise consist of walking around my house, or garden if I am having a good day, and doing some very basic yoga movements while sitting in my chair. I have tried going for some long walks, but I end up in pain afterwards, and then pay for it with extreme weakness for a few weeks (one time for three months).

Before MG hit, I used to run, literally run, up to the top of the local small mountain every Friday. My goal is to someday be able to walk up there again, even if it takes me all day rather that a few hours. I'm getting there.

It might be helpful to identify if you have constant pain no matter what activity you do, or if you only have pain associated with activity.

I hope that helps.