Everyone goes through peeks and valley during there first 2 years, than again as you get older (40 or older). This also depends on when you started training (age) and how your dojo is doing ( big classes, new students, steady student base, etc) as well if you have friends to train and talk about Karate.
Also we get to a point when we still need to work on basics but we are bored of them and think we should be working on other things, more advance things.
Get a full-length mirror and do all your punches, blocks, & kicks in it. See if you are doing everything to your centerline or putting them in the exact spot... The mirror does not lie and will tell you truthfully if you are as good as you THINK you are. This should help you boost your desire to work harder at getting better and your desire to train should also grow
Set small goals, these goals should be easy to accomplice in, a day, week, month or so. If you set a goal of becoming a great fighter (which is a great goal) it will take years and your motivation will be hard to keep up unless you have a dedicated coach and or team behind you.
By setting small goals that you can cross off your list you will keep your motivation high and you will then get to your ultimate, goal no matter what it is... Focus on training, if you are bored with the instructor talk with him in honest. If that does not work than look for a dojo (no matter style) that fits you (you personally not what you think you want, but what you are as a person). The instructor not the style is what keeps you coming back each night or quitting and or getting bored
Motivation also comes from liking what you are doing, and liking what you are doing comes from (in Karate) the instructor and the students, NOT the style..(not until many years later in your training 10-15 years min

. If you don’t enjoy the dojo you are in look for others or try reading about the Budo arts, remember karate, judo, kendo and aikido are really not Budo they are sport arts. read where these arts got their philosophy from (the Budo arts) this to can help you learn and motivate you...
You need to enjoy what you are doing, and not get caught up in the stigma of a style.
I fit in Kyokushin, but I would also fit into styles like Wado, Goju or any other hard style of Karate because I’m an aggressive person and enjoy hard training...
Now I realize that this is a lot to take in, but this is the physiological side to why we do things...
Find out why you are bored and why you need to be motivated to do something you really like doing?!?
If I really like what I was doing I would not need motivation, but I would need new goals and knowledge......
Good luck