During erection the head or the glans of the penis further expands in size and the current state of elasticity of your foreskin do not allow it to smoothly unfold. This gives you pain and discomfort.
Next Steps
Try pulling behind regularly after bath and washing inside initial during flaccid state and after few days during erection. Surgery for circumcision can be avoided in your case unless it turns out to be an extreme case of phimosis.
Health Tips
if you cant help yourself visit a sexologist.