I Was Doing My Daily Rutine When I Feltnon My

I was doing my daily rutine when i feltnon my upper arm like if i had a bad bruse i paid no attention to it till now that i get home it looked like a mosquito bight but it had a dark spot, so i squished it and dry puss came out then blood, now it burns i like if i have a ball inside of my skin what should i do?