Constipation and straining-23m old

Dear Doctor,

My 23 months old son is having severe constipation for the past 3 weeks.He usually passes stool on alternate days.But three weeks back he started passing green liquidish stool thrice a day in small amounts.Stomach was completely bloated and he was in pain.
Homeopath prescribed combination medicine-carbo veg,lycopdium( and 3 more meds all mixed in one bottole of pills)his stomach pain went and it did not look bloated anymore.he gained some appetite.Dr said to continue giving the combination alternating with chammomila(also with other combination meds)and bio tabs 24.However his constipation did not seem to get any better.the paed advised lactulose for a month daily with which we are not very happy about.he also said to give enema whenever he cannot pass stool.He said it was the lack of water.But no matter how much water,soup or papaya he has he is constipated.He has to strain himself a lot and cries out.He touches his bottom probably because the stool is not falling out.Teh stool is like small stones as a big as 2 or 3 marbles.Some times its followed by highly paste like brown stool. He is taking the chammomila nd carbo veg alternately so his appetite is just okay(its not too good and no matter what he has he is very lean and looks very frail).The child is otherwise very active.He takes cows milk once at night but I have stopped that for 2days also to check but no change.He is breast fed.
This homeopath does not use a stethoscope or check the child's stomach.I really don't know how his medicines have worked for us.The homeopath we used to see earlier used to inquire many things and do a good check up.She is not in town anymore. Thishomeopath also suggests taking his chammomila combination daily till 5yrs along with bio 24.(i must say the child has good appetite with it).
The child does not pass gas or burp.
He also has what I understand is post nasal drip(no mucous comes out but I can hear this rattling inside and his nose is congested.I can feel the sound when I can keep my hand on his back).the dr again a has given a combination med kali carb and others with kali mur.

I am so confused..
Please help and advise .

Many thanks and all the help is sincerely appreciated.
Nisha.G