Please help me!!

So I came off the pill 15th October this year. I had a withdrawal bleed as usual and then had a cycle which lasted 36 days I then had a period on the 24th November which lasted for 4 days. It is now the 31st December and I have not had another period as usual yet. I took a pregnancy test on the 28th December and it came back negative. Me and my partner are actively ttc and I used to have normal 28 day cycles but I now don't know what to do and not sure what is happening. I would appreciate any advice thank you.