Q

At times sperm comes out of ny private parts but does not comes out of my underwear so wearing of same clothes except that underwear and after performing gusul and going for namaz is allowed or do i have to change my clothes as well?

بسم الله الرحمن الرحيم

Yes, in this case you can pray in the clothes after having bath and taking off the underwear; since the clothes are clean.

The above reply is in case of sperm, but if the fluid is other than sperm then the ruling may be different. 

Allah knows Best!

Darul Ifta,