Pain in the right side of the pelvis can be due to Acute appendicitis
,Right Ureteric stone,Right sided twisted Ovarian cyst
,Pelvic inflammatory disease
If you are having missed period,it can be due to pregnancy.It can be diagnosed by simple Urine test like Preg Colour test.
Rest of the conditions can be diagnosed with Ultrasound
Please consult your Gynaecologist and take Advice.
Wish you good health