This time of year is the worst for me too, which is not uncommon according to my T. Its summer here but I still have troubles.
With meds, keep an eye on your lithium level, it should be between 0.8 - 0.12, Talk with your doctor about your concerns, your side effects and how well the drugs are working.
What do I do? With time i have gained greater understanding of why I feel the way I do and that has helped. In the short term, developing techniques like deep breathing, count to 10 etc, for immediate relief, if that doesn't work, excuse yourself and go some where to recover (outside, bathroom, bedroom - whatever works). Positive self talk can also help.
I also find that daily meditation (set your alarm for 5 min and concentrate on one verse/ idea/ saying) or yoga can help to decrease your overall stress level.

Hope this helps