Someone please help me

on nov 8 2017 i got my first dose of the depo shot but i didn’t like it at all i had another appointment for my second dose feb 9 2018 but i didn’t go because i decided it wasn’t for me with that being said how long will it take my cycle to come back on ? it’s been 3 months now & the reason i got off the shot was because it made me gain a lot of weight & gave me diarrhea . some people say it takes 6 months for you to get your cycle back but why is that