if you were going to go schizophrenic then smoking cannabis may just bring it out faster, but that's debatable imo, many people with mental illnesses may just use cannabis to cope so the studies may have some confounds. Some people end up with anxiety problems, this is still not certain as many people use other drugs as well. I think the biggest real side-effect from long term use is that life will seem boring afterwards. Other risks are from inhaling all that smoke but that can be eliminated by vaporizing/edibles.
I can't really see cannabis as the cause of your nausea, unless you constantly avoid eating so that you don't bring down your high or something. Could it be something else? If you feel tired all the time, try just smoking at night when you can relax. If you are just burnt out all the time then it's not surprising that you may end up tired during the day, a nap usually solves this.
If you are smoking spice as well, then you can't really be sure what is causing your side effects. I don't know what base the spice is using but the plants they spray the chemicals on may have their own side effects and probably affect people to different degrees. Start vaporizing cannabis, quit smoking spice and I bet most of your symptoms, if not all of them, will subside.
