Trying to conceive no luck

Me and my fiancé been trying to conceive for 8months now no luck I'm starting to think I can't get pregnant because I have high blood pressure and diabetes I'm starting to give up but my sister told me if I have regular periods I can't get pregnant. My period always here faithfully on time but me nd fiance work are opposite and only have sex like once a week sometimes once every 2 weeks. What should I do I need help bad !!!!