Help please?

I had faint positives wed, thur and friday ( slightly darker) but today it extremely light and digital negative with.FMU, experiencing sl nausea, sore boobs and v mild cramps.

I think im right to assume its a chemical? I have never had a positive before, what do I expect? Im really upset as I feel lost on what to expect.., will I pass something or I go straight to a period? Im on letrozole with pcos so relay on ovulation to have a period and scared I will take it by accident with the miscarriage (if i should have one) rather than period, im around dpo 14-18 as a guess? My app thinks im 3 days late X I just want to know whats normal is anyone could help whos on letrozole and experienced this? X thankyou