I'm 17 years old and I have been playing since I was 7. My problem is that lately I have noticed that my lip has a permanent embouchure mark and sometimes it even hurts.
That's a problem. Here's what might be happening. Depending on what register we are in, we tend to tip the horn to help facilitate the process. My guess is that you are pitching the horn up and driving the top portion of the mouthpiece into the teeth. This could be due to more pressing repetiore or longer sessions practicing. Never the less, the situation you have is usually due to excessive pressure. In some situations, there's been an injury to the lip and an abcess develops. If there was/is and open wound to that area, stop playing and let it heal.
I thought that I was using too much pressure but I have been working simple exercices in the middle and low register trying to use very little pressure for some days now and the issue continues the same.
I'm going with excessive pressure. Let the lip rest for a week and after a week, begin with long SOFT tones and as you do this, slowly pull the horn away from the lips while maintaining (as best you can) a good sound. This will help activate the corners of the lips.
I use a Bach 1 1/2 C
Do you find this size a problem? If so, after a week's reast, try a medium size mouthpiece, 7C and see how it feels.
Hope this helps