My EBF LO was a constant spitter from a few weeks after she was born. She was a happy spitter though, and gained weight like crazy (because she nursed every 45 min during the day and every 2 hrs at night since small frequent meals helped soothe her tummy) so we didn't worry about treating her reflux at first. Then she had a couple of episodes that appeared to be Sandifer's Syndrome (http://en.wikipedia.org/wiki/Sandifer_syndrome) and as she approached four months she could not stay asleep for very long because her tummy was so painful. So we decided treatment was necessary. We did three things:
1. Put her on Zantac efferdose tablets. This seemed to help reduce the frequency of the spit ups.
2. Bought her a Tucker Sling (http://www.tuckersling.com/) so that she could sleep in an elevated position. I'd had great success putting her to sleep in her car seat but I really didn't want to continue doing that, so we spent the $$ for the Tucker Sling and it was worth every penny.
3. I changed my diet. I found that when I was thinking of my diet in terms of "can't eat X,Y,Z (or ABCDEFGHIJKLMNOPQRSTUV or W!)" that I got kind of sad. So instead, I chose the following foods as what I _could_ eat. I limited myself to lamb, turkey, squash, potatoes, pears, rice, and millet. I saw improvement that very day, which was surprisingly rapid. I know it wasn't just my imagination because when I went off the diet a few weekends later my LO got worse again. So while a number of folks will tell you that very few babies with tummy troubles are actually reacting to what Mummy is eating, in our case that was absolutely part of the problem. (Looking back now, I'm thinking that the primary source of her reflux was onions.)
After a month or two I was able to go back to eating whatever I wanted, and we stopped having her in the Tucker sling at about 6 months and stopped the Zantac at about 8 months. She's still nursing at 18 months, and has never shown any signs of being allergic to any solid foods (and we've given her pretty much everything, including peanut butter, shellfish, eggs, nuts, etc.)
Since you are a vegetarian, you may have a very difficult time getting enough nutrition if you are limiting your diet. Please be very careful if you do this, and I would highly recommend seeing a nutritionist to make sure you are still getting what you need!
Remember that this will pass and your baby will get better. I personally have a hard time with the theory that a baby with a sensitive tummy will have an easier time with formula, since breast milk is designed by nature to be easily digestible. That being said, if you do find that to be the case then please do not beat yourself up! I would continue pumping as much as I could so that your supply stays up, and I would periodically offer him breastmilk (ideally directly from the source, but if he has trouble latching on you could give him pumped) and see if he's grown out of his tummy troubles. I have heard about babies that for whatever reason had to be bottle fed from birth that were offered the breast at a later date and were able to figure out how to latch on, so if your son has been doing it for four months the chances are good that he'd be able to go back to the breast.
Good luck to you! Reach out to La Leche League and/or a lactation consultant and get direct help and you'll both get through this.