I updated to v1.7.0 and since then Minecraft keeps crashing. I can't use it for more than a few minutes before it crashes. eg

If I enter a world it crashes and I lose the last build I've created.

When I go into the game on the screen where you can choose the worlds, it freezes straight away.

Is there a bug with this version? What do you recommended? if I uninstall and reinstall, will I lose all my worlds/builds?