I am a 25 year old mother of three. On October 23rd I delivered my third baby. No complications. On December 7th I had an IUD put in. Afterward I had very heavy bleeding for a about 10 days and have been spotting ever since then and at times the spotting gets a little heavier. I went for my checkup on the 28th and my doctor said that I was bleeding from what looked like an "injury" to my cervix but that the IUD looked fine and did not need to be removed and then prescribed an antibiotic. I am still bleeding and was wondering if this could be something serious and how long should I let the bleeding to continue until I take serious action for medical help.

What kind of IUD was put in?

I would go get a second opinion. If there is "injury" to the cervix it should be treated a little more aggressively than just some antibiotics, depending on the type and extent of the injury.