Baby Constipation. Many ml i can give?

My baby is 1yr 3 months, he s passing hard stools since 4 weeks. He s stressing a lot while passing motions and cries sometimes. I am giving A-Zdrops(1ml) every day since a week as per paediatrician's advice but not seeing any improvement. My family members are advising to put castor oil to baby. Is it okay? If so how many ml I can give? His diet is as below 9:30am: Ragi/rice Dosa 12:30pm : 1 apple 2pm: rice, baked carrots/other vegetables 6pm:  1 orange and some dry fruits 8:30pm: Dosa/roti He also has not gained any weight since 1.5 months(he weighs 9.5kg). He s very active and playful all the day. Also, I have put a syrup for worms a week back as per the doctor's suggestion. Please suggest if anything needs to be added in his diet to make his potty smoother and is it okay to put castor oil to baby.