Hello
I really appreciate your concern
Of course you need to be concerned but you need not to worry much about this
Looking at present condition you might have injured your foreskin during the  
masturbation or may get infected if it was healthy previously.
If I were your treating doctor, I would have advised you to keep it clean and apply antiseptic ointment 
if it doesn't improve or worsens than I would have ordered few investigations like blood for 
hemoglobin, CBC 
Liver and 
kidney function test, blood sugar and urine culture or an 
ultrasound if need be.
you may require a course of anti allergic or antibiotics drugs under supervision of doctor
In my opinion Application of hot packs will help in healing
If it doesn't improve or gets worsen than you must see your doctor for physical check up and a course of antibiotics if need be.
Hope this answers your question
If you have any more queries please feel free to write back to me, I will gladly answer you 
Best wishes