TTC baby # 2

Me and my man of 7 years are trying to try for baby # 2 and just running on empty and out of hope !!! We have a 5 year old little boy !!! Had no problem getting pregnant with him !!! Now that we are trying for this one !!! It's like it feels like it's not gonna happen ... We got false hope !!! I could of swore I was pregnant !!! Sore boobs they started leaking !!! And I got super bad head aches !!! And felt sick some times and tired all the time I took 3 home test all negative went to the doctor and also the 4th test negative !!  And then a week later bomb there my period was like 2 weeks late !! My periods have not been normal since Iv had my son !!! But we want to know what we are doing  wrong or what we can do to get pregnant !!! And not give up !!! Like should I start taking a prenatal to help my friend said I should and my doctor !!! Even before I'm pregnant to stArt it while we are trying ???