Suggest Treatment For Infertility

My husband and I have been trying to conceive for over 2 years and we haven t been successful. We have been tested by our physicians for various things related to infertility and all of the tests have come back negative. We have been charting my cycles and have started keeping track of my basal temperature. We exercise regularly, eat healthy, and we do acupuncture fairly regularly. We are both overweight but our tests have all come back very good (especially mine). We can t figure what is the issue but, as crazy as it may seem, we re wondering if sex position has more influence on conception than we were lead to believe. As far as penetrative sex, we have only had woman on top and I wonder if that might have some effect on us not being able to conceive (as strange as this is). I know I am probably way off but I ve been too embarrassed to ask my doctor this question and the question has been nagging at me.