You should check out taking Cara babies on! She has a course you can buy but she also offers a LOT of free info on her website and her Instagram! I bought the course and frankly didn’t benefit as much as I wanted to, but the free info has helped us a lot!
Take him to the pediatrician or hospital
I found nights.with.nat on IG really helpful and willing to offer free tidbits of advice.
Huckleberry app offers a sleep plan made for you specifically by professionals, and it's only 13 (pm, but you could just get it once and end subscription). I found it really good. A private one would cost a lot i imagine, I doubt you'd get free advice as people don't tend to do that.