If your diet previous to the vegetable diet was low in fiber, your cramps may have been due to the sudden increase in fiber from the vegetable diet. Also, vegetables that are members of the cabbage family (broccoli, Brussel sprouts, cabbage, and cauliflower) increase intestinal gas. Did you eat any of those during the 1-week diet?
Your intestinal tract is one long muscle that rhythmically moves food along for further digestion then absorption and whatever wasn’t absorbed is waste. Fiber increases this movement and the lack of fiber slows that movement.
So if the fiber of your diet was suddenly increased, you may have felt some cramping. Instead, I would recommend a gradual increase of fiber over 2 or 3 weeks so that your intestines can adapt slowly. It sounds like you are off the diet now, but if the cramping continues, see your doctor.
Did you increase your fluid intake? Insoluble fiber found in whole grains and some vegetables absorb water in the bowel and effectively clear out your intestines by increasing the bulk of stool. Whereas soluble fiber found in fruits and dried beans/peas increase the water content in stool making it softer.
The part of your question I am concerned with is, why did you choose a vegetable diet to lose weight? What were you planning to eat after you lost weight to maintain your lower weight?
If you indeed need to lose weight follow a balanced diet from each of the My plate Groups and fewer calories (not lower than 1200 calories) than you eat to maintain your weight before you started losing weight. Vegetables are low in calories and high in vitamins, but by themselves do not cause weight loss.
Second, while vegetables are nutrient-rich foods, they are not high in protein and even the best source of protein, corn, is lacking in an amino acid lysine. Certainly not a good weight loss plan to go on long-term.