Starting baby on solids, constipation?

I had my baby on the hungrier baby milk and his poo was getting a little harder, but he was still going twice a day, which was more than usual, it wasn’t bothering him either, so i assumed it was all ok.

Now i’ve started to give him solids his poo is like rock hard and only doing a few "marbles" in the morning and a few at night, if that. He’s getting a little bit of baby rice in the morning and a little bit of rusks at night, not much though, about 3 baby spoons of each mixed in with his milk (baby spoons as in the weaning spoons you buy).

What can i do about the constipation? Will it go away itself? Should i give him some cooled boiled water, i was told to this when he was a newborn and very constipated. Will he be getting more dehydrated now i’ve introduced the first foods?

He’s on 9ozs of hungry baby milk (was taking this every 2hours) and since introducing baby rice and rusks he’s been taking the 9oz every 4 hours and only taking 5/6oz in the morning and at night when i’ve been giving him the rice or rusks, which i think is a great improvement so he won’t be feeling as full and bloated as before.
It’s nothing to do with you how old he is etc, i was actually advised by my doctor to start him on baby rice as he was taking 9ozs of hungrier baby every 2hours, he’s 3 months next week, which was the age that babies got fed solids at until they said that they will develop all those allergies which haven’t been proven to be related to feeding early. I don’t know why i’m explaining myself, i’m asking a question, not asking if you think my child is too young.
He is eating from a spoon, i feed him the rice/rusks and then give him the rest of his bottle. He takes it very well from the spoon, doesn’t spit it out, he swallows it, which is an indicator that the baby is ready for food. Yeah he was taking that amount, if your a mother, you’ll know the difference between hunger and other things like, boredum, the need to suck etc etc. He doesn’t have reflux.

Incase you didn’t notice i’m actually asking a question about constipation and solids, how to relieve it and if it’s normal, i’m not asking if it’s right that i should be giving my baby solids at 3 months. Yeah i’m asking advice on that, nothing about his age etc.
and i replied that i dont give a f*ck what you think, i’m giving him baby rice because i was recommended too, actually it might be said that 6 months is the time to give them solids, but why on the baby food jars etc does it say 4 months plus???? You never said stop giving that poor baby food, you were just being a nosey judgemental cow, i’m asking if it’s normal that they should get constipated, you answered with something completely irrelevant.
Forgot to add, he sleeps through the night, so doesnt’ feed through the night but feeds every 2hours during the day and screams for more after he’s drained the bottle.

I asked a similar question before i asked my doctor and EVERYONE said that i should do it if i want too, and most of them had the same experience, all their babies are fine.
http://www.homemade-baby-food-recipes.com/ready-for-solids.html

All the websites i’ve looked at have stated this, my baby is doing all of this. He might not be able to sit up alone, but he can sit up for a few minutes and he can turn his head, lift it up, sit up with someone holding him and his head doesn’t flop for at least 5/8minutes