Constipated baby ?

My LO since birth has always been a few days in between BMS 3-4 at most and sometimes clay like stools doctors haven't been concern but between the last 4 days he's has two stools really hard stools ! And it's hurting him he has been trying to poop all day and finally has but it's hard, doctor said that when he starts solids it would become more regular and softer but my little one seems to be in so much pain and he's been spitting up a lot more