Why am i having pain in my right leg?

More details please: There are dozens of reasons someone might have pain in their leg. We need much more detail about the type of pain, exactly where it is, what makes it better or worse, your health history etc. to have any chance of giving you a helpful answer.

Depends on history: If sudden onset, without any trauma or exertion history, and if worsening steadily and substantially, suspicious for vascular emergency in your leg, and needs evaluated in er asap. If low level ache, after activity, or only in certain part(s) of leg--either muscle group or band-like distribution running down leg, more likely muscle or pinched nerve--which just need dr check to recommend treatment.