Thanks for posting your query.
The Depo is usually a very effective method of contraception
and has a very low failure rate.
However, if you are concerned, the best thing is to do a pregnancy
test and put your mind at rest.
Bleeding irregularities are quite common with Depo and is a common problem with it. You have been on it for 3-4 years and maybe you should see your doctor for a general check up. The headache and tiredness
may be incidental and not related to your contraceptive
method. However, when the Depo is used for long periods, in excess of two years, it can cause weakening of bones, for which your doctor may order a bone density
scan, if he thinks it appropriate.