Trouble conceiving

Hello my name is Jennifer I'm 26 and I have a 6 year old daughter. My boyfriend and I have been trying to get pregnant for over a year with no luck. My question is does anyone know what I can do to increase my chances of conceiving. I've taken prenatals, I have lifted my hips after sex. I've been trying to loose weight by working out nothing to strenuous just walking sit ups stuff like that. I quit drinking soda...I'm at my wits end