Don't bother with the injection - the side effects are horrific!
Obviously some people are absolutely fine and if you are then you're very very lucky, but if you do get side effects you're stuck with them for over 12weeks until the injections worn off..
The ones they don't really tell you about properly when you go to the doctors include:
Evil mood swings, Depression, Acne, Weight gain, It can generally lower your immune system and its generally not recommended for people under 19 because it can affect your bones and this could lead to osteoporosis in later life.. also it can really mess up your periods: you could be on for well over a month or you could be on for 3 days every single week or they might completely disappear and then you get worried your pregnant.
Stick with the pill and or condoms..much less hassle in my opinon!