Pain in hamstring and weakness in front of thigh

Hi, I am having a bit of pain in my left hamstring which I think might be related to a back problem I had a couple of years ago - which left me with a very weak left leg - which could not bear weight when bent - I had to take stairs one at a time as the left leg needed to stay straight if it had weight on it. This weakness gradually recovered - but I was always suspicious that it had not fully recovered. I am doing a bit more exercise now - cycling about 30mins a day - doing a bit of walking, I do gently ballet once a week too. I am now getting a persistent sore hamstring which I am wondering might be having to work hard to compensate for the muscles in the front of my leg not working so well. Does this sound at all likely? If so are there any exercises which I could do to strengthen the front muscles? If not does anyone have any other suggestions!