Trust your "mama gut" ... which it sounds like you're doing with the ECI evaluation and ENT visit. I started thinking my son's hearing was off around 8 months and sure enough, he had middle ear fluid which was causing him some hearing loss. We worked with our dr. to see if the fluid would go away (sometimes it takes a few months after an ear infection) and it didn't so he had tubes put in at 13 months.
We also had an ECI evaluation at that point because I thought his speech was off for a 13-month old. He was evaluated and found to have a speech delay (probably caused by the short-term hearing loss). They can tell those types of things ... even in children under 2.
So, while things may just work themselves out as others have suggested - why wait? There are resources available and you can get your son on the right track now. Even if it turns out there is no speech delay per ECI and no hearing problem per the ENT at least you've had those two things professionally evaluated and will probably feel much better about how he's doing.
I think you're doing the right thing - kudos to you. Also, congratulations on the upcoming new addition to your family!