IRREGULAR CYCLE/VFP/BFN...longest you've gone?

What is the longest you have gone (or heard of) with someone testing positive? For instance, I didn't have a period at all in August and I got a faint Positive today on a pink test...and then right after I got a BFN on a blue test! I've been on Mirena for the past 5 years, took it out in March. I expected an irregular cycle but it's getting weird. I also just found out that I have diabetes and was prescribed Metformin a week ago.

So has anyone been a month late with their AF and got a BFN ..then wound up being pregnant after all?