Could I Be Pregnant After A Missed Period, Negative Test, And Light Spotting Following Regestrone Use?

Hi I missed my period on Apr 01 so I took urine test on Apr 05 which is negative. Started using regestrone for 5 days each per day. After 2 days I see only spotting for 1-2 days in brown/dark colour. Could I be pregnant? Should I test again? FYI I have used regestrone earlier 3 times where I got a normal period. Also I took letrozole on last period.