Sounds a bit weird, it took me 8 mths to get AF back, with bothe of mine and I stopped BF with number 1 at 16 weeks.

The only oither thing I can't suggest is start testing everyday with an OPK it may be a bit expensive but you may then get an idea, but you'd probably have to do it 4 a couple of mths to know the difference IYKWIM?

Good luck hun