My Right Leg Is Very Weak And It Drags. I

my right leg is very weak and it drags. I have to hold on to the rail going up any stairs. at night I feel like my leg in going to explode with pressure. I am 65. I can ride my bike everyday with no problem. What kind of doctor should I see ? ( my brother died at the age of 43 from ms, a very severe case of it for 5 years in a nursing home) just thought i would mention it ) I also have back pain. I don't take any meds for it I just deal with it. I don't believe in alot of pills etc.