implantation bleeding?

So AF was due 03/20 and I took a hpt on 03/19 which was 11 dpo which was negative. I had a bit of spotting on 12,13,14 dpo which was the 19, 20 and 21 of this month. I didn't even need to use a panty liner as it was so light and either brown or pink. So I took another hpt this morning and it was also negative. I'm so confused as my last 2 periods after coming off the IUD were full on periods. I also have had no cramping and have been very tired and nauseous on and off. Was this just a tiny period or could I still be pregnant? I'm worried if this was a tiny period it could impact my ovulation for next month :( thoughts?