I am 24 years old, after severe depression/mania/psychosis from age 12-20 I tried many Antidepressants/mood stabilizers/anti psychotics and even ECT(with no effect), I finally got the right balance of 225mg of Venlafaxine in the morning(8am) and 300mg of Lamotrigine at night(8pm). I have been stable with limited mania/depression and no psychotic features for 6 years now. I weighed 97kg when I first started this dose of Venlafaxine and Lamotrigine 6 years ago, however over the last 11months I have slowly lost weight through exercise and healthy eating/portions. I have noticed as this was happening in hindsight I was/am feeling more tired, I find it very hard to wake up in the morning and just generally tired(but not in a depressed way) Also my heart rate during exercising has been pretty consistent at 170 beats a minute but I just took it again these last couple of weeks and it has been around 200 beats a minute and afterwards takes about 10-20minutes for it to start to go back to normal range. Feel quite like crap until it calms back down. Could this be due to the amount of medicine I take and my weight being smaller(75kgs) ? and causing side effects now cause the dose is too high? Should I talk to my doctor about possibly reducing it a little?
What are other peoples experience with weight loss and these medicines? I don't want to take just my doctors word I want to make sure I fully know as it is my decision not just his.

Also I have no physical illnesses, generally healthy according to GP