Mild cramping in Uterus and lower back after period

I'm 35 this year and haven't had children yet.

On November 2016 after a routine ultrasound, it was discovered I had two large chocolate cysts caused by endometriosis on each ovary.

I had surgery to remove the cysts and endometriosis on March 2017.

Earlier this year I had an ultrasound which showed my uterus as healthy.

For the past three days after my period, I've been getting this mild cramping and lower back burning pain when I'm sitting, especially after I eat. I'm also passing gas, burping, and wanting to poop more often.

I can't tell if this is a digestive issue or something wrong with my uterus :weep:

It's scaring me that I've got mild cramping after my period and this back ache whenever I'm sitting down. Not when I'm standing.

Does anyone else get this mild cramping and back ache for a few days after their period? I've never had it before and my mind is racing with panic!