I'm 35 weeks and 5 days pregnant I'm having menstrual like cramps a lot and pelvic pressure. What could that be?

Preterm labor! The cramps could be contractions of the uterus. Normally they are supposed to happen at full term (37 weeks plus) so you should be evaluated to make sure you are not at risk for giving birth prematurely!
Early labor. Sounds like you are experiencing early labor! i would recommend going to your maternity hospital to be checked out, as 35w5d is still preterm. Best of luck!