Trying!!

Hi I have been with my boyfriend 3 years and I still have not gotten pregnant. I really do not track when I ovulate but I downloaded this app in hope that I will get pregnant. My boyfriend has 2 kids prior to me but I been with him for 3 years so now I'm starting to get frustrated knowing IM the one with the problem. I have a question on the days that it's green on my calendar which is giving me the percentages of chances of pregnancy, do I have to have sex everyday on the Green Day's or when I can? I'm going to be 28 years old and I want a baby so bad. It hurts me that I haven't :( I would like some advice