Pelvic tightness is present during pregnancy
as well as before periods, due to increased vascularity of uterus
If your periods are not yet missed then it may be due to congestion of uterus occurring prior to periods .
But if you want to confirm if it is due pregnancy, you can perform urine pregnancy test at home. The result will be positive only about one week after fertilization and ovulation,when the embryo implants and the placenta attaches to the uterine lining.
The pelvic tightness due to other reason like Pelvic inflammatory disease
, infection will have other symptoms - per vaginal discharge
, abdominal pain