Ttc #3 ovulation strips all negative


I have 2 beautiful children age 4 and 5 and got pregnant 1st and 2nd month with them. I am now almost 33 and have been trying for #3 for 7 months. I started taking ovulation strips for the first time ever and they are all negative. I get the slightest- can barely see- line around my predicted ovulation but it's VERY faint. Anyone else experience this? Trying to decide if I should go to the dr or if I need to just stop stressing and keep trying.