Advice PLEASE!

So my periods are always pretty much on track with the calendar. Well last month I had my normal period, heavy like usual, then come two weeks later here is AF again! And not just spotting, it was a heavy 5 day period. Now this month I've completely missed my period and have no signs of it coming. Does anyone know why this could be? I took a pregnancy test last month that had a faint line, I took another the same day that was negative so I haven't re tested but I'm not really TTC. I also have a heart shaped uterus. Any information would be helpful!