Thanks for your query,based on the facts that you have posted it appears that you have blister
over glans penis
Mostly this could be due to infection or allergic reaction
to soap that you are using,
You need to take broad spectrum antibiotic like Cefexine along with anti inflammatory drug like Diclofenac
Do not attempt to pop it out yourself .It will get cured with use of antibiotics.
Ensure to wash your genitals with warm water twice daily.