is very effective if taken during the early days of a period and if you have taken it later on in the cycle, you may not be protected. If you are due for your regular period now, this spotting is likely to be a scanty period as is often seen with depo shot. Else, you need to be tested for pregnancy
through estimation of serum beta-hCG
titres. You would also be in need of a trans-vaginal sonogram to sort out the situation. Irregular cycles, intermittent spotting and absent periods are all seen while on the depo shot. Hope you find this information useful. Wish you good health.