Front brake lever will not stay tightened I have a 2011 Trek Cobia with Hornet brakes. About an hour and a half into my trek through the woods this morning I noticed that (once again) my left brake lever was hitting my knuckle when I fully compressed it. I had noticed it compressed too far two days ago so I adjusted the position with a 2 mm allen wrench. I notice that the brake lever is also closer to the handlebar than before. These are hydraulic disk brakes.

I've had this problem before, a few months ago I noticed that I could compress the brake lever almost all the way to my handlebar, which was unusual (this is all with the left lever by the way, my rear brakes are fine). Eventually my front brake lost all power and compressed fully to the handlebar with no resistance.Since I was relatively new to mountain biking I just took it to my LBS and they bled the brake. A few minutes into my next ride the same thing happened. Note that the brake stayed fully functional until I used it. I got that same LBS to bleed the brake again, but alas, my brake lost power again. This time I took it to another bike shop to bleed it for a third time, and it stayed. I had no problems on any future rides.

So, on to the problem at hand. When I noticed the problem two days ago (just in my room) I readjusted the position of the lever with a 2mm allen wrench (as stated earlier) and I also decided to reposition the entire mechanism relative to my handlebar so I could get an easier reach and so my wrists would drop more, making going over obstacles easier (saw it on a video on YouTube: 
                
            ). The reason I bring this up is that I may have merely noticed the brake lever compressing too far and touching my knuckle when I used it because I just raised the brake lever. So I'm not sure if this is a new problem or not.

I have never noticed any discharge on any part of my front brake system, not on the cable, not below on the caliper, not by the brake lever. Could there be a small enough hole that lets air in but doesn't let liquid out? I'm going to reposition the lever again with the 2mm allen wrench and see if it happens again. Do I need to take apart the housing, could there be a "screw loose" or something along those lines?

Thanks for your patience, I feel like I rambled on a bit, but I just wanted to be clear and give all the relevant details I could.

P.S. I have no money, so going to the bike shop is kind of unavailable at the moment.

Thanks for any help!
Do these brakes have a small adjuster screw just behind the lever blade? If so, that is a reach adjustment. It allows you to adjust the distance of the lever blade from the bar. Sounds like it's turning on it's own. Some brakes have this issue. What you need is the tiniest amount of blue (workable) loctite/threadlocker on the threads of that reach adjuster bolt. Very important that you don't get it anywhere else or else it will gum everything up. I would apply it with a needle or safety pin to ensure precise application- squeezing it directly from the tube may prove messy. Once that sets, the lever should stay in place.