I'm pretty sure I'm doing something wrong.

I'm a right-handed guitarist, playing a right handed stratocaster (I think..) shaped guitar,
I usually have it resting on my right leg when playing sitting down,

however after maybe 30mins of playing, I get these sort of pains on my mid to lower right side

Does anyone else get these pains or am I doing this wrong?

I play on a LTD MH-50, if that's any help..