Hello. I had protected intercourse (always) with...

What is the treatment of stopped menstural cycles
The menstural cycle is a physiological process in which the ovulation play the key role of inducing hormonal changes that will allow the uterus to grow an endometrium that will slough if no pregnancy happened in cases planning for pregnancy. In case your periods did not come and you are having protected intercourse and negative pregnancy cycle then the cause would be a failure of ovulation and inability of the endometrium to slough in the shape of menses. To look for whether the ovulation failure is temporary you are adviced to take 5 days of high dose progestron only pills in a single daily dose and after stopping the pills you are expected to have your menses back. if not you should consult a gynecologist to look for the cause ot ovulation failure
Investigations 
After proper physical exam, cbc should be done to look for anemia, Hormonal profile including TSH, T4, Estrogen ,Progeston, FSH, LH to look for any hormonal imbalance. on the other hand you should underwent a transvaginal US to assess for the endometrium and both ovaries to look for ovarian cysts 
Causes 
Premature ovarian Failure
Ovarian cystic disease 
Hormonal imbalance 
Thyroid dysfunction 
Our advice 
You are adviced to have a proper consultation with a gynecologist