Life is never perfect; it is often fraught with difficulty, and it refuses to conform to our wishes and our expectations. This seems true for all beings, yet truer if you are living with a severe mental illness.
Those without mental illness might have other difficulties. For example, it is not an easy time for soldiers, who, if they survive, are coming back to the US with post traumatic stress and numerous other problems--not to mention permanent physical injuries. Other people are oppressed by socioeconomic problems, and never get a chance at a good education, or at an opportunity that would allow them to rise out of poverty. Still others must face terminal illnesses, in which case they are looking at impending, certain death.
The point is, nearly everyone has their own set of difficulties. Many wish they could exchange the difficulties they experience for those of someone else. However, this does not change the basic predicament, which is, according to the Buddha, that "All Life is Suffering."
However, Buddhism also states that all things are impermanent; this is a good thing.
If one is having a difficult time in life, one should know that the difficulty will not last forever. Conditions could get better through luck, through being helped, through random probability or through one's own efforts. One can at least count on things not remaining the same.
It may be helpful to clarify a difficult situation in one's mind in order to know what exactly is bothersome. When you can pinpoint the issue that causes emotional upset, and when you get a "map" of how it affects you (e.g. what part of the body is tensed up, and the specific thoughts that comprise the suffering) the issue can sometimes be set aside or can even be resolved on an emotional level.
Sometimes one's path is difficult over a long stretch of time, but this does not mean that things will always be this way. If you gain understanding about what makes you unhappy, you then have the option of working to correct that thing, or accept it. It is harder to accept something that bothers you if you don't have clarity about what the thing is. This is where paper and pen come in handy.
If the difficulty relates to the symptoms of mental illness, one should realize that the brain changes over time. A symptom that is foremost at present could get better over a longer period of time, or a better medication to treat it could be invented.
If the difficulty is that of medication side effects, one should realize that side effects sometimes get less severe with time. The human mind is designed such that eventually you may learn to ignore a medication side effect that is constant. (This does not include Tardive Dyskinesia, which is awful but which doesn't have to ruin one's life.)
If something in life is awful, it might help to just pay more attention to something else. If you have had a bad day, forget about it. You could watch your favorite TV program, or maybe go to the ice cream place and get a scoop of ice cream. I recommend "housewives" which is so mindless, so superficial, and so irrelevant that it will make you happy to be yourself. I also recommend Thrifty brand ice cream which is still available at Rite Aide.
Life's difficulties arise periodically and usually, at some point, change. Sometimes you just have to muddle through a difficult period, and hope that things will be better in the future.