What Causes Pain In Lower Abdomen?

I received the Depo shot January 21st of this year. After having continuous bleeding I decided not to get my second dose in April. I am severely anemic and have to use panty liners or tampons because I am still suffering from side effects of the Depo. Lately I've noticed using tampons cause pain in my lower abdomen and side. I have no idea why this started happening. Please help!