Hi, Welcome to Healthcaremagic. I had gone through your question I can understand your concern about your about your allergic rash. As you said you are repeatedly itching or scratching it please avoid it. It can cause infection to your allergic rash. You can use anti allergic or steroid cream like betamethazone local cream for itching or take anti allergic like levocitrizine orally. Now your question is what causes pain and disappear after you start walking. See when you are sitting the bruises are guarded by thin film of clot, that thin film is direct in contact with nerve endings underline because of that when you stand there nerve endings signal brain and you feel pain, so that you become aware of the problem. When there is repeated stimulus that too for a non serious condition signal vanes off (it is a pain path way mechanism). Finally you don t need to worry about this much, it is a normal thing. Keep your wound clean, don t scratch it any more, you can also use FUCIDERM cream to prevent it from infection. Hope the answer to your query. Regards Dr Muzaffer Hussain Parray