Knee and shin pain

For the past few months I've been having severe pain down the center of my shin and both knees. It's a crippling pain that only happens in short bursts where I cannot stand on that leg when it happens. It is completely random when it happens. Whether I'm playing a sport or just resting and sitting still, the pain is always completely random. Nothing provokes the pain. I've visited the doctors office prior to now and they insists it was just shin splints. I've done everything they've advised me to do after insisting back it wasn't shin splints considering I know what they are and I don't get a pain when I take steps. Like I said before, it's completely random. It has been a few months and I'm getting worried whether it could be something with my nerves especially since it is happening and getting worse in both knees. What should I do and what could it be?