You shouldn’t be smoking from such a young age, your brain still in development and using drugs can disturb this process.
However, having trouble to sleep and having weird dreams is normal after stopping smoking. That will normalize some time – just try to have a consistent routine of sleep; around same time each day, having 8 hours of sleep, sleep in darkness, without a TV/phone light on your face.
About your weight loss, I am not a specialist but I think it is caused as a result of not feeling weed hungry anymore. But that’s just a guess, maybe seeing a doctor would be the best in your case.