My husband said this and not sure what to say or how to help..

First question is he a good dad and if the answer is yes it could be postpartum depression men get it as well maybe talk to him and see if he needs any support and then speak to the doctor

My partner also is struggling with postpartum depression, I spoke to him and asked if he would consider counselling it took him a while to agree to it but I think having a child is such a huge adjustment it's ok to need help.
If your in the UK and your partner is employed he should be able to get free counselling sessions

Low mood, loss of interest in hobbies he just seems really down sometimes and getting frustrated with small things especially to do with our son.
As someone who has depression and has done lots of counselling and therapy it's easy to spot when someone else is struggling so it