yes,it can be due to the periods,stress
or gut-related.you shouldnot be taking chances.
please go for a urine pregnancy
test at home--urine pregnancy kits are available over the counter in the pharma stores.
also,get an ultrasound
abdomen and pelvis. you can use pain-killers. and the next time , see to it that condoms are used during sex. you need more sexual awareness.