Not sure how far along I am

A

Right I had my normal monthly visitor at the beginning of December on schedule and it was as it is normally and lasted 5 days (baby dancing all the way through December as you do)

January comes and my monthly is due but I was extremely light and it lasted 2 and a half days if that. Took a test and got a very faint positive followed by three negatives so I took this as a no and carried on. This month nothing so left it a week or so before I tested which came back positive (woohoo)

Now I have an appointment on Monday and she will ask the date of my last period. Do I go by January or December. Could January be an implantation bleed and I am much further along than I am assuming, just not sure. Has anyone else had this?