I've got one on my left thigh. Dermatologist told me it's a fatty lump.
I'm also 2 stone overweight with thighs that look like those big gammon hams you buy at Christmas. I try and avoid looking at my thighs too but they are hard to miss these days!
I have health anxiety too and am always looking for lumps and bumps, which is how I found the one on my thigh.
Make a (non urgent) appointment to see the GP to get it checked out just in case but I suspect he/she will tell you that it's a fatty lump.
I've started walking to help my anxiety and hopefully shift some weight.
You are a teacher. Could you walk to and from school? Or is that a stupid suggestion with marking, books, etc.