At the risk of over stepping, this sounds a little like the depression talking, rather than logic. I know - I've been there...ok, still am there most of the time.
You weighed in on Sunday and had lost 6lbs, and you say yourself that you broke the cardinal rule by weighing yourself too early. If you'd waited till next Sunday, you may have found that you dropped another pound or two from the six. You're doing so well, why not give it a couple of weeks to see if it does have any impact?
I'm sure that once you get stabilised on the meds, you'll be more ready to deal with whatever the effect is, and you'll find a way to work through it.
My philosophy is one day at a time. Try to do one day of sticking to it, even though you're feeling a little down. Then try again tomorrow. If you fall off a little on one day, no biggie, start again the next day. IF the drugs do add a little weight, it will still be less than it could be if you stick to your plan.
Right now, nothing is set in stone, stick to your plan so that when the meds kick in and you start to feel a little more stable, you'll still be on track.
Remember - it's just a diagnosis that you can't control - you
can control what you choose to do about it. The Japanese believe that if you have a nightmare and you turn in the dream to face your fear, it's no longer a fear. Turn and face it - let it do it's worst - you're strong enough to make it.