Suggest Treatment For Irregular Periods And Difficulty In Conceiving

Hii,
I am trying to get pregnant from last 6 to 7 months but every month i get my periods and from 5 to 6 months my periods date is also changing, like for example first it was 6 of every month them after 3 months it came to 12 and not again it is changed and came to 25, please can u help me that how can i get pregnant also i want to mention that my first baby is 16 months old, every month i get very depressed when i get my periods, please help me and let me know that how can i get pregnant, my first pregnancy was easily conceived but now i am not conceiving, please help me, should i take folic acid and other than folic acid what should i do, just today i got my periods again :( please help me, Thanks