Hi,
This is one of the paradoxs you will find as you continue in the arts. The simple fact is that in order to get better, you will need to repeat the same actions/drills/techniques etc over and over again, and that can lead to a certain degree of boredom.
Frankly, you could study a different art each month or so, constantly experiencing different training methods and techniques, but you will gain absolutely no usable skill or ability whatsoever. So, in you want to be good at your chosen art (Muay Thai), then the simple answer is to keep training (through the current boredom and plateau), and in that way you will improve.
But to help you minimise your boredom, you may want to vary your home training. Spend some time working on just footwork, sometimes doing some impact work (if you have a heavy bag, or the ability to hang one), or a workout without techniques (running, weights, skipping, swimming etc). You may even increase your home time in lieu of one or two nights out at the various gyms.
As for having a goal, it seems you already have one ("I want to get better"), you may just need to fine-tune this a bit. What do you mean by "better"? How will you know when you are better? There needs to be a method of measuring your growth, and with that in place, your goal can be easier to see and attain. So, what we need to do is come up with a way to measure your success. Do you compete? Or will you measure it with something less tangible to outsiders (such as feeling more natural in your technique, being less physically taxed by a big workout)? This is a question for you to answer.
I'm not going to recommend a new art for you at this point, for the reasons listed above, but if you are feeling that you aren't getting the attention you need to improve, then by all means have a quiet word with your instructor. Simply say that you are wanting to focus on improving (maybe one particular point to begin with? Say, hand combinations, or kicking power?), would they mind watching you and offering their advice? I have approached my instructors in the past this way, and have had students of mine approach me in the same fashion, and it is always a very good result.
Other than that, I wish you luck and success in Muay Thai.