Any diet takes time . Some vegetables may not agree with you the same way they agree with other people, either in your family or friends in your community. Sometimes the combination of foods may not be a great thing to have in your stomach at the same time. You need to find what works for you. If we lived in a world with no boxed/bagged/prepackaged/etc... foods whatsoever, people will still have to watch what they eat because anyone can have a reaction to anything. Vegetables and fruits are incredibly powerful. If you're in a lot of pain, don't push yourself to go further and assume it will be gone. Try to eat what you were eating before with as much tolerated fruit/veggies as possible. After a month or so, add in one more vegetable a day. It may take forever but may be the only way for you. It kind of was to me... I've been on my "diet" since last August and have posted pictures every few months or so with very small improvements. I'm doing this so as not to push myself.
I found that salads were causing me stomach and bowel pain. Despite people saying that you should eat salad every day, I simply can't. My gut/bowels can't handle it and no matter how much I chew it comes out runny and green. No matter how hard I try, I can't tolerate organic/garden grown/spring mix/ etc. lettuce. Spinach is the only leafy vegetable I have no problems eating, next to kale which is too bitter for me to have every day. Unless my salad is a small side next to something that's easy for me to digest, such as fish, it goes right through me. Salads cause me the most pain, so I avoid them. Maybe one day I can have them again.
It is your stomach, right? Usually stomach reactions are very quick. If the sensation is delayed for an hour or so after you eat and you're bloating in your lower torso, then it may be your bowels that's not agree with you. Maybe your not producing enough stomach acid to keep up with healthy foods yet, and the undigested food is upset your bowels. Maybe it's both. Maybe it's neither and you happen to be allergic. An allergy test is 20 to 45 bucks I think, give or take insurance. I would recommend a food allergy test, maybe that'll help a little (It didn't for me but I was still glad for peace of mind).