When my son was your child’s age Isaiah had the same problem what i would do is tickle his butt with a q-tip it stimulate and relax his muscles, that would work sometimes. Other times it would be really bad i had one scare where his fesses was so hard that i had to help get it out i went to his pediatrician and she  gave him suppositories.  That too work as well, I know it is very painful for them and it’s hard for us to see them go thru that. Your baby is too young for anything oral but i believe you should talk to your child’s pediatrician and ask then about the suppositories.  Good luck.