My shower has a wall mount single lever faucet similar to this: http://www.cn-faucet.com/Wall-Mount-Single-Lever-Faucets-141.html
Over time, it has become more sensitive and now, in most angles, gravity pulls and turns it off, unless water flow is very high. If I turn it to get very hot or very cold water, it becomes less affected, and at only hot or only cold, (when it's almost horizontal), it can stay on with a very slight water flow.
The lever has a screw that holds it to the faucet, and I haven't found anything else to touch.
I use it now without the lever, and it's quite steady (hard to use with the hands, indeed; I usually put the lever to turn it on or change water temp, and then put the lever aside).
What could be the problem, and how could I fix it?
The faucet itself:
You can see the screw at the bottom of the lever; this screw bites the black plastic piece of the faucet to keep it in place; I don't think this is related to my problem, though. In the center of said black plastic piece there's a screwhole, but there's no screw in it.
If a more detailed picture of some part is needed just ask for it.