What Causes Short Periods And Difficulty In Conceiving?

hi i have a 2.5 yr old already. and since sum time trying fr 2nd child i ma nt getting pregnant, this month i hv put on wt as well, feet swollen, felling tired soon, sore breasts but all tets showing negative, i hv started having short periods only 2 days since 4 months but nothing happening. wht to do plz help