Suggest Treatment For Infertility

My partner and I have been trying to get pregnant for 6 months now. His brother had a baby at 21 and also has a 1 year old. He and his fiance had no problems and it happened at the drop of a hat. His sister had a baby in November last year and she also had no problems getting pregnant with her boyfriend. There evidently isn't anything wrong with fertility on his side of the family! I have aunts and cousins on my maternal and paternal sides who have had fertility problems. I'm worried it may run in the family. I feel like I must have something wrong with me and such a failure. How long should we leave it before approaching a doctor for tests etc.?