Hi.. Thanks for the query.. Allergic reaction to aspirin at the site of allergic reaction is due to inflammation caused at the site of reaction.. The allergic reaction can be treated by taking antihistamines like Claritin or benadryl or allegra twice daily for 3 days.. Keep the area of the piercing clean and apply steroid based ointment on it in order to reduce inflammation and bump.. In case of pain you can take anti-inflammatory painkiller like Ibuprofen or Advil.. You can apply numbing gel containing lignocaine or choline salicylate over the inflammed area for relief from pain.. Do not remove or change the jewellery you are wearing over the belly piercing till the area heals and becomes painless.. Do cold compresses not directly by placing ice but wrapping ice in a clean and dry cotton cloth and putting it over inflammed area.. In case you find discharge or pus formation which are signs of infection you need to take antibiotics like augmentin or clindamycin for 5 days and apply antiseptic ointment over the area.. Hope this helps.. Regards..