Why is my period still here...

Tara • Happy wife and mother to a beautiful baby girl born 09/15!
Hi ladies, 
​  So I missed a couple of days for my pills and then doubled up on them like I was supposed to. I have been on my period since December 21!! That is 3 weeks tomorrow. I don't understand what is going on and my doctor really does not have any answers. Has anyone had this happen to them? I know this is a place where women are normally trying to conceive but my husband and I are not going to try until August. So for now I am on the pill and have been for almost 16 years. This is the first time it has ever happened and I don't know what to do. It's like nothing I do makes it stop. I keep taking my pills like I am supposed to but I am just about done with this months pack and still having the longest period EVER. I did a blood pregnancy test and I am not pregnant so that's not it. Thank you all for your help!