Trying to get pregnant with baby number 2

Hello ladies me and my partner are so lucky to have a beautiful little girl who is now 16 months old we have been trying for a year to conceive again but had no luck unfortunately and we have no idea why im 20 and hes 26.. we havent spoken to anyone about this before but it just breaks my heart to think i might not conceive another baby for my little girl to have a sister or a brother any tips on how you conceived a second?