OP, hugs from here too. My DC has a mild form of bipolar and is barely 100 pounds, so we don't experience the physical fear, but watching the depression and heartbreak and worrying about suicide.... well that by itself is difficult.
do you have any counseling for yourself and family members? Have you sought out any NAMI or DBSA family support groups. I assume your DC has a psychologist as well as a psychiatrist. That is important. DC needs a place (other than you) to be educated about the illness, how to manage symptoms, how to deal with stress, maintaining social rhythms, long term expectations and goals (plenty of people out there who are highly successful despite and even because of their bipolar).
I really encourage you to look at bpso.org and sign up for their on line support group. It is the best thing I have found because it is only for family members of those with bipolar (as opposed to major depression, schizophrenia and/or other major mental illnesses). The BPSO support group creates connections to a large number of people whose loved ones are going thru exactly the same illness and can share all kinds of experiences. I found it extremely useful, both in terms of emotional support and in terms of practical advice. I do not think I would understand the illness today as deeply as I do without BPSO group.
Of course, understanding the illness helps us cope. Your son sounds like he needs a med adjustment and that you are progressing with that. Meds can take time to settle and have their effect. You should ask more questions about this. Lamictal is a mood stabilizer with a known anti-depressant quality, so I do not understand why, if your DC is already manic, he would not be moved to something that is a more established, proven mood stabilizer like Lithium or Depakote. IME, doctors like to use newer drugs, which often don't have a well-established history, proven efficacy in controlled trials, etc. My understanding is that the drugs like Abilify (the anti-psychotics like Zyprexa, Seroquel also) should be prescribed as add ons to squash oncoming mania, not for long term mood stabilization. Other drugs like Lithium and Depakote are considered the gold standard for long term mood stabilization. If you are concerned that the med mixture isn't working, Johns Hopkins has a second opinion service (or clinic, I don't know exactly what they call it). Of course, JHU is renowned for their mood disorder care. If you can manage it, you should really be working with a psychiatrist who specializes in bipolar and sees a lot of bipolar patients.
That said, adolescence is hard because of rapidly changing hormones and weight, which means that it's harder to find a stable med mixture because the child is changing so rapidly. I also find that people are quick to dismiss or overlook early signs as typical adolescent mood swings. It's very difficult to tell the difference between typical adolescence and rising symptoms of mental illness. In this respect, I find it very helpful to keep a journal of symptoms, and depending on your child's age, they can participate in this too.
It's difficult when they get mad. A lot of things get said or done that are regretted. I just try to remain calm during the tantrum. Usually afterward there is some expression of regret. I explain that I know that it is the illness and not them and we love them regardless. We talk about ways to channel anger, ways to handle things before they get too big. Sometimes journaling can help you figure out triggers or warning signs -- lack of sleep, problems at school, friendship, etc.
I highly recommend books by Kay Redfield Jamison (who is bipolar herself and a renowned mood disorder specialist).