Depo shot question??? im very scared?

okay so this is my second baby, i got a 15 month old and currently 37 weeks and 6 days pregnant, im 15 PLEASE NO RUDE AND MEAN COMMENTS. i know i ******* up bad. anyways, my doctor recommended me to get the depo shot birth control 6 weeks after baby is born. she said the iud shes too scared to put in me because, if i was to change partners, or my boyfriend cheat on me, it can cause life-threatning infections...and ive always been scared to do birth control, as of the side effects, such as irregular periods, spotting, irregular bleeding, i dont want to start bleeding at school or somewhere where i cant get a pad or whatever, headaches, bitchyness... i tried nuva ring a while ago, i could not sleep with a blanket i was very bitchy, i was sweating bad, so i took it out and had like a week of bleeding, then missed a period the next month, then the month after had a normal period, and i dont want to go thru that bullshiit again. and i heard so many bad things about the depo, i mean , i know my best friends girlfriend is on the depo, she said it is like a million percent effective on preventing pregnancy, but made her gain a lot of weight, which you can tell shes chubby, and talks like a person whos face is chubby, ya know? and i heard it causes bone problems later on in life, or during that time, and causes very heavy bleeding for a long time, i heard it causes a lot of crazy side affects, and im very scared. what happened to you when you got the shot???????????? i will admit when i met my boyfriend he turned me into a "freak" and i guess its cause im pregnant, im very horny a lot with him.