I stick to one FM throughout before my boy was 1yrs old, he took NAN, so I stick to it till he is 1yrs old then change to Friso....but if you decide to change, if your daughter is not showing signs of discomfort shoud be ok to change FM. As for not pooing for 3 days, is tht a really major concern to you? When she was on NAN HA2, did your daughter poo everyday or ...?
But some babies dont't poo everyday....
As for the cereal, mayb you want to try other brands of cereals? there are plenty off the shelf or mayb also those bottled food? or organic porridge? you can let your daughter try and see which she prefers?
Hope this helps
We are all learning together.....but most importantly, decide what is best for you and your daughter, dont't stress