Preparation for elimination diet

Hi! I've had digestive probs for years, and it's been getting worse, to the point where I vomit on average once every 3-4 weeks for no clear cause, have grown used to having diarrhea 1-6 times/month, frequently experience painful cramping in my gut when my bowels move, and often have bouts of painful and/or embarrassing gas. I have also been experiencing ever-diminishing energy levels and fatigue, as well as foggy thinking. I suspect that I am intolerant to certain foods but haven't been able to definitively pinpoint anything (lactose test was neg), so I've decided to try an elimination diet. I read a lot about it on the forums on this site and elsewhere, and my former doctor recommended it to me, so I'm pretty sure it will help answer some questions.
For a month before I actually do the diet, I'm eliminating foods that act like a drug on the system: alcohol, sugary junk food, and caffeine. I'm on day 4 of that, and I feel terrible. That's why I'm posting this message. Is this all in my head? I didn't expect to feel this way. I see black spots, I feel exhausted, experience deja vu and dizziness throughout the day, and while there are parts of the day where I feel pretty normal, it can collapse all of a sudden, leaving me fatigued, barely able to drag myself to bed for a nap. Last night I woke up with terrible nausea which kept me up for an hour. I am reassuring myself that this is due to withdrawal from those 3 things (I had not been a heavy user of any of the above, but consumed those things on a near-daily basis in moderation...or so I thought), but I'm wondering three things:
1) Am I harming my body by going off all 3 at the same time, and is feeling this yuckky a normal part of the process?
2) Are these symptoms a sign of some other health problem that I need to attend to?
3) Is there anything I can eat or do to help myself feel better during this transition phase?
Any thoughts/advice would be most appreciated.
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