Fractured Femur

I fractured my left femur on April 2012, in a bike accident. It was broken into 2 pieces in the middle. I was operated on the same day with IM nailing, with a pair of screws at the top( below the hip) and bottom( above the knee). My surgeon suggested me to walk with a walker for about 5 weeks (non-weight bearing)

Two weeks post the operation, I started with Physiotherapy. At present, I am able to bend my leg inwards and lift my my leg almost as much as my right leg.

When my went for my check up, 10 weeks post the operation, the doctor has asked me to use an elbow crutch start putting weight on my leg ( 50% body weight), as much as i can bear. He also asked me to start strengthening my quadriceps by trying to lift weights( 500 grams) with the leg.

Now its been almost 13 weeks and I have been doing the same. I get slight pain at d feature sight sometimes while putting weight on it, but it gradually goes away in like 10 seconds or so. Is that normal ??

Also, having a look at the X-ray, there is a still a gap in the bone( almost as much as after the operation), but the surgeon tells that my leg is healing. How is that so ??

I hope to get a response from you at the earliest. Thanks a lot. :)