Constitutional Remedies - how long should I give it?

Hi,

My 3 month son has gone through a few const remedies for his reflux and we aren't having much luck - our homeopath changes the remedy after a week or so of adminstering - is this right? How long should we wait before deciding it's the wrong remedy? He has gone through calc carb and lycpodium and is now on Antim Crud. He seemed to improve somewhat under lyc but didn't last very long.

These are his symptoms:

He is avery restles sleeper - this is my main concern because he hardly naps for more than 20 mins during the day and wakes up frequently during the night - he seems very uncomfortable while lying down, constantly moving his legs and head. Sometimes nursing helps him back to sleep - other times changing his position. Quite often though he ends up waking with a fit of screaming and cries until I get up, calm him down and then nurse him.
He is very itchy which I think also disturbs his sleep. He has a dry scalp and pimples(with white dots in the middle) and red blisters (eczema) predominantly on his forehead and the areas around his eyes(eyebrows,eyelids,under eye area). He doesn't seem to have any outbreaks anywhere else on his body. He rubs his eyes constantly, scratching himself usually resulting in cuts that scab over.
His spitting up seems to have improved under the remedies - he doesn't vomit as much but I know the reflux still bothers him because he is constantly gurgling and swallowing - he also makes gagging/choking faces during sleep. He's been quite gassy of late as well, passing a lot of gas when I press his legs to his chest. Burping him usually results in some milk being spit up and he rarely feels better after burping. He is exc breastfed.
His nose/throat seems perpetually congested. When he cries a lot, his nose starts running. He's a noisy sleeper too, you can hear his breathing.
Generally he is a very smiley baby, doesn't have a problem with strangers and has developed quite well. He is gaining appropriately, has reached all his developmental milestones. Talks animatedly when happy, responds very well to music. He gets upset just before he's going to spit up and after nursing. When he's happy, he doesn't mind lying on his back, he kicks his legs and arms and talks and laughs.
My homeopath has recommended Aethusa as the next remedy to try - is it ok to keep giving different remedies? Will this negatively affect him at all?

Sorry for the long post, appreciate any help at all. Thanks