Dr. Edwards was absolutely on track when he told you that both the medications that your dog is on can and sometimes do cause digestive upset.
And I completely understand that it's hard to know why Lakota is crying...is it from the pain in his back? Is it because his tummy feels bad? The way to figure it out is through trial and error....if he starts crying again, go ahead and give the Mylanta. It works about the same as the Pepto that Dr. Edwards suggested you give and I think a tablespoon would be appropriate for his size.
If the Mylanta doesn't help, you might want to try feeding him a little something with the pills when you give them to him. Some dogs become less sick feeling if the medicaiton is given with food...try to make it something really yummy...not his hard kibble...(I tend to give my dogs a little peanut butter on bread when I have to medicate them).
If this routine of feeding him at medication time and giving the Mylanta don't seem to make the crying problem decrease, then you may want to consider calling your regular vet and seeing if there is a pain control option that would make him feel better...that would get his pain more in control for him so he can be more comfortable.
I hope this helps.
In my experience dogs don't get real 'spacy' on the Tramadol. We use it very frequently in the clinic where I work (we do a lot of orthopedic surgery) and I rarely see that sort of effect with the dogs.
I absolutely agree that it could be the pain in his neck that is causing the whining. I'd definately talk to my regular vet about something stronger.