Is it mandetory to wash after ?

Well there aren't any police that will come around to check and see if you washed, so I don't think mandatory is the term you need. Douching is not necessary at all, however, washing isn't going to harm you at all. Chances are you are irritated by the material the condom was made of, or possibly the lubricant used on it. Washing up should be limited to the outside parts of you, using plain soap and water only. If you wish to sooth tissues, you can pat on witch hazel with a clean cotton pad afterward. None of that is going to harm your skin. Irritation of the tissues makes them more susceptible to infections, so leaving anything that irritates there can cause more problems than washing it away will. For cleaning purposes, stick with plain soap and water. The soap should not have deodorants or perfumes, nor should it be antibacterial either. Be sure to wipe/rinse with clean water to remove any residue, and then you can wipe with the witch hazel if you like. The only other thing to consider doing is leaving the area to get some "air" time, meaning you leave off the undies at least during the night. That should solve your dilemma.