It seems as though everything you do reminds you of your ex. And if the two of you were together for a while, then even going out can be a problem because you most likely have mutual friends. This makes doing even the most routine tasks more difficult, and--to put it mildly--you're a mess at work. Yes, the break up is taking its toll.
Right now you have a choice to make: either try to get your ex back, or move on.
If you want to work things out with your ex then there is some good news in that the vast majority of relationships can be saved. It's going to take some work and you will have to follow a good plan, but it is possible if you are willing to do whatever it takes. There are plenty of guides available on how to make up with an ex, so get one and make it happen!
Perhaps you just want to move on. If so, that's great, too! The first thing to do is let go of any guilt you may be feeling because of it. It's your life and you are the only one who can decide what is best for you. If that means going ahead and living your life, then so be it.
We have already mentioned that a break up impacts all areas of our lives, so it makes sense that you would want to get past it. It can take some time, but it can be done.
A good start is to break off all contact with your ex. The less you have to deal with them, the better. If that means not answering the phone or not checking your email for a few days, then don't do those things. It's only temporary, but the positive effects will last much longer. But what if your ex won't leave you alone? Then you have to put your foot down and let them know you want nothing to do with them. If they are stalking you, then get help.
Another thing you must do to get past a break up is to avoid gossiping about your ex. You may want to tell other people how awful your ex was, or how it was their fault you broke up, but don't do it. This only prolongs your mental attachment to them. So, make it a rule to not spread and not to listen to gossip about your ex.