Ongoing vomiting??

I'm at a loss as to what to do...my 6 yr old female cat has always had a sensitive stomach from the time I adopted her when she was under a year. Ongoing vomiting, soft stools, hairball problem. The hairballs have seemed to lessen a great deal, but about a month ago, she started throwing up a lot. At least once, sometimes 2 or 3 times a day. Sometimes it was very early in the morning (3 or 4); sometimes right after she ate; sometimes when I was at work. This time it's been more bile-like vs. hairball. In addition, right before T-giving I realized she was constipated. The vet did an x-ray and ended up giving her an enema, although she said she wasn't severely impacted. She also gave her an anti-nausea shot. For the next week she was great - no vomiting. Then it started again, so I brought her in for a full blood work-up which came back totally normal. She's eating normally, isn't hiding or low energy - it's just this chronic vomiting, and less frequent stools. I started her on probiotics and digestive enzymes yesterday and pray that that will help...I should add that I recently got a weekend home about 2 hours from my place in the city and I take her and her brother up there every weekend. She hates the car ride, but once she's there she loves it. I'm wondering, though, if the stress of the car ride has screwed up her stomach. According to the traditional vet, the next step would be a barium x-ray, endoscopy, etc. but my holistic vet who I brought her to last nite doesn't think that's necessary yet. My question is - do you know how long it takes to the probiotics/enzymes to start to work? Any advice would be greatly appreciated...I feel so awful for her and just want to solve the problem!