You are suffering from missed period for last month with lower abdominal pain
Depot shot is very much effective in preventing unwanted pregnancy.But there has several side effects like irregular period,prolonged infertility
after discontinuation,wt change,headache etc.
First of all,do a Urine/blood test
for B-hcg to confirm/exclude pregnancy. If negative,do the followings:
USG lower abdomen and some hormone tests like thyroid profile,LH/FSH etc to rule out underlying pathology if any.Stress/anxiety,hormonal imbalance,wt gain/loss,thyroid prob,irregular eating habit may causes delayed period. So consult with your doctor to take suggestive measures.
Take Tab DROTIN DS or other anti spasmodic medicine to get some relief.
Avoid stress,take healthy diet with Vit-E & Folic acid
supplements,control body wt and proper sleep.