Hey ladies - I am taking an antibiotic for a never ending cough (left over from a cold in February)... Anyway, when I picked up my script yesterday, I chose to splurge for the expensive clear blue advanced ovulation test. Yesterday test said low, today says peak. I only took ONE antibiotic. The fine print for the sticks says antibiotics with tetracycline could affect results. It doesn't say if it makes it high or low, ect. Could I actually be ovulating? Could I go from low to peak in ONE night? today is day 9 since my last period.