hello, Depot shot is very much effective in preventing unwanted pregnancy. But there has several side effects like irregular period including long time amenorrhoea, prolonged infertility after discontinuation, wt change, headache etc. Need to rule out other underlying pathology like ovarian cyst/ thyroid disorder/ obesity/ psychological factor etc (as you trying to conceive for more than 6 months) by means of USG pelvis, thyroid profile, blood sugar & prolactin level, other hormone assay, tubal patency test to rule out blockage, serial follicular study for monitoring ovulation, husband semen analysis etc. Consult with infertility specialist regarding this for suggestive measures. Ovulation occurs approx 14 days before the next due date. Ovulation prediction kit is very much helpful to predict ovulation & you can prepare for unprotected sex. Avoid stress, take healthy diet with Vit-E & Folic acid supplements, control body wt,maintain personal hygiene and need proper sleeping. Be well & take care.