Hello,
For confirming the status of pregnancy, if you miss your periods then you can test 1 week- 10 days after you miss your periods or you can test for pregnancy by a highly sensitive pregnancy test 10 days post ovulation with a sensitive ( 20 - 25 mIU ) pregnancy test. Also I would suggest you to get your serum HCG levels estimated since this is more specific than urine for pregnancy tests. The HCG (it is a hormone) levels rise only in pregnancy and its presence will confirm the status of your pregnancy.
I hope it helps. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
a friend of mine was on the depo shot as well and after getting off it her cycles were very irregular she would spot all the time until she went back on the pill to control it, but you should still take a test