Suzy,
i see where (& why) hotasfrick is coming from but one thing that caught my attention in reading his post & checking yours was
"or if you experience a very very happy period of time and then fall back into depression, then go back to your doctor"
since you're pregnant (ooops just checked your post date & I guess you're a mum again now - congratulations!!!!)it is almost certain that you are going to have some big highs & some probably/possibly unexpected lows, this is normal for any woman regardless of anything else that is or is not going on in her life.
When we give birth we experience a huge high often followed by a big low, because of huge hormonal changes & because of what absolutely no-one can prepare you for as words won't do it - the huge pressure of responsibility for that tiny scrap of humanity that you adore. Then too some women suffer post partum depression & don't adore, don't even want anything to do with their babies.

the range of emotions is different not just for each person but for each birth

& has nothing to do with either bi-polar or depression it just happens & no-one can say who will feel what.
so if you suffer extreme or new emotions that worry you now that you're a mum again, join the rest of us, but do talk to your dr he/shesounds like someone who will listen & hear you & respond appropriately, still if in doubt second opinions can be reassuring.