Based on your description, you're using a different launcher than normal. Normal MC launchers don't have a "Force Clean" button. Try downloading the original launcher from here- https://minecraft.net/download
Click on the blue link that says "Minecraft.exe". Start it up and login, then in the bottom left it should say "Ready to download & install Minecraft 1.7.2".
This is probably a performance issue.
First of all, try different video settings. Such as turning Fancy to Fast if it's on, no smooth lighting and render distance to minimal chunks. Just try scrolling through them and see what the effect is on your performance.
If that does not help, check your ram allocation using F3, and look in the upper-right corner of the screen. If that gets above around 70-80 %, (depending on preference) add more ram to Minecraft. (Remember you need to make sure other programs can still run without Minecraft consuming all the ram so that might be a problem)
You can do this in the profile editor under Java settings (advanced). In JVM Arguments you will see that you can input how much ram you want Minecraft to be running on. In this box you fill in:
"-Xmx2048M -Xms2048M" for 2GB ram
"-Xmx4096M -Xms4096M" for 4GB ram
To add more, add 1024 to the numbers for an extra gigabyte.
eg, 4096 (4GB) + 1024 = 5120 (5GB)
If that does not help, try deleting your .minecraft folder in it's respective location.
Mac: /Library/minecraft
Windows: Press Windows+R, type "%appdata%/.minecraft" and press enter.
But make sure you back the folder up!
Many people have used this technique for similar problems without: eg. Internet connection, so the launcher could not re-download the folder. This is also the folder were world saves and texture-packs are stored so again, back it up first.
if that does not help you need to wait for new vidcard drivers that might solve the problem.
Best Answer
@sf kind of already answered this, but here in a bit longer:
This most likely happens, because you have set Sprint to "Toggle" in Options->Accessiibility Settings.
In this mode Minecraft remembers if you activated (or deactivated) the sprint mode, even across servers/worlds. If you want to play with that setting, pressing your sprint key (usually Ctrl) switches you between sprinting and not sprinting. Otherwise just change the setting back.