Looking for answers

I am 23 years old with a 4 year old boy & me and my fiancé have been trying for 6 months now . I have taken ovulation test and everyone of them show I am ovulating on time every mon like I should be but nothing ; he was in a 5 year relationship before me and they did try and conceive and was never successful . When they broke up she had gotten in another relationship and about 3 months in she conceived . He is very convinced it’s him and have been looking for options on how we should start trying to do things different or any fertility options for him and i . I just need options and help I’m so tired of seeing one line