Getting trough a breakup can be very painful and I don't think I'm familiar with a greater pain that heartache.
If you still love the girl and want her back, then you should know that this is very achievable.
As long as you know what to do and you have a proven plan to follow, then it's almost 100% sure that you can get her back.
However, what's the point of getting her back, if you guys brake up a few weeks after, because you run into the same problems as before? You should take some time and think about what went wrong and if it is something that you can prevent in the future.
If it is and if you still want you girlfriend back, after thinking about this stuff, the go ahead and do whatever it takes to get her back.
A word of caution: Don't wait for too long, every day, your chances of getting her back gets smaller.
Therefore, you must act as soon as possible, but on the other hand, you shouldn't do anything at all if you don't know what you are doing.
You see, in most cases, what seems natural to do (for example to call her up and tell her how you are feeling) is simply wrong and will only drive hr longer away from you.
I really recommend that you go and talk to a close friend who has lots of experience with women and let him give a plan to follow.
You need to know stuff like:

• When to call her
• What to say
• What not to say
• How to act
• How your mindset should be
• What to say if she wants to meet you
• How to act if she's dating someone (and how not to act)
• What you should do to get her attention and get her attracted to you

Alternatively, you could go and get hold an "get you ex back" guide, that will guide you through each step, often this is even better than using a friends advice (especially if he doesn't know what he's talking about).
Whatever you choose to do, be sure to do it very soon as time is against you in this case.