I went no flour no sugar and got badly constipated

I'm sorry that's happening for you.

Usually, if it's related to dietary changes, the main things that can trigger constipation are:

* Too much fiber, too quickly. (Bodies tend to adapt better if fiber is increased gradually.) However, getting too little fiber would be a common cause of constipation, too. For most people 25-35g of fiber ought to be adequate, but a combination of soluble and insoluble fiber is good for you. It's the insoluble fiber that tends to most affect digestive throughput (whole grains, fruits & veggies, beans, bran, etc.).
* Inadequate hydration, not just water, but other fluids we may consume. Essentially, if there isn't enough liquid to keep the waste soft, it doesn't move through the body well.
* Inadequate fats. This is somewhat common among people who're trying to lose weight, because fats are calorie dense, and people cut them in order to reduce calories. But bodies require a certain minimum of fats to function well. One of those functions is smooth digestive throughput. (Something in the range of 0.35-0.45g of fat per pound of body fat will be adequate for most people. Things like olive oil, avocados, nuts and seeds have especially healthful types of fats that many people underconsume.)
* A little less common, but too little exercise can contribute to constipation. Things that move the midsection can be especially helpful.
* Also less common, specific nutritional deficiencies can increase the probability of constipation. Magnesium may be helpful, in particular, if there's not enough in the diet.
* At the margin, some people find adding pro-biotic foods to be helpful. That would be things like yogurt, kefir, raw/unpasteurized sauerkraut or kim kim chi, miso, raw fermented pickles, kombucha, raw vinegar, and more.

If you have been constipated for a long time, with no bowel movements for multiple days, leading to discomfort, it would be a good plan to consult your doctor. Severe constipation is a problem and could be a symptom of other worrisome health conditions. Your doctor would be a better source of recommendations for even over-the-counter medications, rather than random people on the internet. If you are already eating a large amount of fiber, tell your doctor this. Often, they may assume you are getting too little fiber, because that's very common.

4 days trying keto did that to me. I was OK as soon as I stopped restricting my diet though. I think my body got a shock! Its scary though, right? Hope it resolves for you soon.