My boy has had vomiting issues on and off his whole life. Out of curiosity, is it always partially eaten food or is it only partially eaten when he gets the pepcid? does he ever vomit just bile? when you say that it is usually early in the morning, is it consistently the same amount of time since he has eaten? how long has this been going on?
If the food isn't fully digested and you haven't given him pepcid, recently, (pepcid could slow digestion some) then I would look to the food you are feeding and try something else. Like others said he could have an allergy, although it sounds more like just an intolerance, to something in the pro plan. If you do some serious research into what goes into dog food and the very lax/nonexistent regulation of them, it could be just about anything. A lot of people love Orijin and I agree its a good food, but it doesnt work for everyone. as much as I wanted it to work for my kids, it just diddnt. (My frenchie had chronic skin infections for 15 months while on the food. they went away immediately after I switched her.)
Here is a website to get you started on Dog food research :http://www.dogfoodproject.com/
My second Idea is that he is still young (you said 6-8 months, right?) and some dog's digestive systems dont mature as fast as they do, causing puppies to vomit from time to time when they eat to much. You could try 3 meals a day and see if that helps.
Another idea, is he getting up, early in the morning, and being really thirsty so he wonders to a bowl and drinks too much? Lots of dogs will vomit after drinking to much water.
If he is vomiting bile at say, 2 am every morning, I would put some "cookies" or milk-bone-like treats (but not milk bones- use something healthier) next to your bed and give him some like 10-20 min before he normally vomits. this could help if he is doing it due to an empty tummy.
Along that line you could also try feeding him dinner, later in the evening or right before bed.
another thing about Pepcid. In general it is a very safe drug. (my frenchie was getting 2 a day, for a while) However, in humans it has shown to lower the seizure threshold. My boy was getting pepcid on a daily basis and started to get seizures more frequently. When we took him off the pepcid, they went from 2 times a month to maybe 1 a year or less. When he has episodes of feeling "vomity" we give him a 2 week course of prilosec. I think we have done that 3 times in the last 5 years.
You could also try adding a probiotic and/or digestive enzymes to his diet to help. Just go talk to someone at your local health food store. In general I am skeptical of probiotic supplements that are not refrigerated (they are live organisms, so I dont really understand how they can live on a shelf for so long). You could also try adding yogurt, but it wont have as high of a bacteria count, as well as some dogs dont agree with dairy. (my dogs get yogurt with every meal)
Oh I forgot one other thing. Is there a possibility that he could have ingested something that he cannot pass? A partial blockage that is stuck in the stomach can cause dogs to vomit partially digested food, especially when they have been laying down. Even Greenies or rawhide could potentially cause this.