Dachshund Tummy Trouble

One of our dachshunds, Byron (now 6 yrs), has had bad tummy aches since he was about 9 months old.
The first time it happened I was lying on the bed with him when suddenly he started to yelp. I picked him up to see what was the matter and he started to growl and snap and writhe around like a dog possessed! This lasted for a few minutes and not knowing what was wrong with him I rushed him to the emergency vets who kept him in overnight. The next morning they said they could find nothing wrong with him and said he probably just had a stomach ache.
These episodes have continued pretty regularly ever since. There are times when he just has a very bloated hard feeling belly and he tries to stretch it out by holding a sort of play-bow position, and other times where he has similar episodes where he suddenly leaps up from where he's lying and rushes around the room screaming. These occurances are often followed by him then throwing up.
Over the years we have fed him quite a few different foods ranging from dry biscuits to wet food and most recently to raw feeding. They don't seem to have made any difference to his stomach problems. He is currently (and has been since January) on Natures Menu frozen raw diet with a chicken wing thrown in every now and then. I had hoped this feeding would settle his stomach down.
His most recent episode was at 5am this morning after having slept all last night on our bed. He suddenly jumped off the bed screaming (I say screaming as it is a very loud, ear piercing and frightened sound), ran around the room and eventually hid behind our laundry basket (still screaming). When I rushed to get him out and rub his belly like I always do, I discovered that he had wet himself. This is the first time he has done this. (I appreciate that he probably just had a very full bladder and lost control during the excitement!) When he stopped whining I took him outside and he threw up as usual.
I have mentioned his tummy troubles to the vets a few times over the years and they never seem very concerned and agree that they are probably just tummy aches and that he probably just plays up for the attention.
So sorry to waffle on forever! I just want to give you as much information as possible as I'd really appreciate your opinions as to whether I should be concerned about him or whether he really is just a drama queen, and any suggestions you might have??
Thanks in advance for any help you can offer!