pink spot

I had no periods due to Hypothyroidism n started on meds a month ago.
We are TTC and yesterday I saw blood in CM and then on tampon light pink. I was happy that my cycles are coming back on track but  that was it. I had nothing more than a few pink drops. 
We have been baby dancing almost whole month,taking folic acid etc
What does spotting mean and how early can I test for Hcg? Since I don't have regular cycles  I cannot say my exact date of period.