I've fractured my nose a month ago ,
Great question - and very common. After nasal trauma, just like trauma anywhere else, you will have subsequent swelling as the tissue gets inflammed and tries to heal itself. The issue is two fold - 1) the blood circulation in the face is fantastic. its part of the reason why things can heal so well (and so much faster in relation to other parts of the body) on the face. that being said, as your heart rate increases and your blood pressure rises with exercise all of this blood supply to your face will increase. As this happens, the areas trying to heal (which will already have an increase demand in blood supply) will get flushed with more fluid. this is an oversimplification of the mechanism, but you get the idea. as you continue to heal, the amount of swelling you get after workouts will decrease. also 2) in order for things to heal quickly, they need to rest. think of breaking an arm, and having to be in a cast for 4-6 weeks for example. the nose is in the middle of your face, and as such, a large majority of the muscles of facial expression are connected in one way or another to the nose. as you go about your daily routine, your nose will shift in miniscule amounts - certainly enough to prolong the healing process. this is also part of the reason why it can take a year for things to settle after a rhinoplasty. putting both of these together, you can see why your nose swells after exercising following trauma. unfortunately the best thing for you to do to speed up the healing is take it easy :). use how you feel as a guide - if you feel swelling and throbbing, thats your body telling you that you are not quite ready to push it that hard. it will improve. and it will go down. once the swelling resolves, if you would like to fix the broken nose because you are having difficulties breathing or you do not like the way it looks, thats a totally different issue! i hope this helps.
It is common to have nasal swelling after nasal injury and often occurs after exercise. I highly recommend a consultation with a physician to evaluate the extent of your nasal fracture and injury. I also recommend avoid heavy lifting and contact sports while your nose is healing. Best of luck.