Wheatfreedude is spot-on with the 125-135HR zone for fat burning (if you haven't had your own determined by way of a VO2 metabolic analysis which measures bodily oxygen consumption and carbon dioxide production during exercise). Working in your fat burning zone will reduce the stress and impact of exercising on your body and, even if you cannot run in this heart rate zone now, a month or two at it and you'll happily be jogging/running in it as your body adapts to it. It will also ease the damage done to your knees through impact.
You eat a lot of fruit in your diet it seems - do you get ill a lot? Simple sugars in the form of glucose and fructose, commonly found in fruit, chocolates and milk, lowers the efficiency of the immune system where as more complex sugars/carbohydrates such as maltodextrin, potatoes, sweet potatoes, and gluten-free versions of grains have less of an impact. Eating the simple sugars as in fruit and ice cream may be having a compounding effect on your gut and subsequent inflammation...thus the weight gain. (this may sound stupid, but weigh yourself before eating or exercising in a morning, 5-10 mins before eating the ice cream at night and then 60mins after the ice cream and assess the differences if any - it could be an inflammatory response). Please don't do this for every meal or food - just see what happens this once.
Also running, or any form of exercise, places a stress on the body. Scientific studies have demonstrated that exercise and stress increase gut permeability (causing holes in the gut lining allowing larger undigested food particles amongst other things into your bloodstream). If you already have coeliacs then you already have a permeable gut and running may be making it worse (Please note that I am not saying that it definitely is, just that it is possible). If this is the case then the apparent "weight gain" may be an inflammatory response and thus you need to address the inflammation.
Have you had a food intolerance test done? Its a test that assesses your immune system's response to foods and NOT an allergy test. Food intolerance involves IgG antibodies, traditional allergy involves IgE antibodies. If you have not already, find yourself a good clinical nutritionalist, they will be able to help you....you need your whole lifestyle, dietary intake, supplement regime assessed. S
Supplementation with things like L-glutamine can help, but PLEASE REFER TO A SPECIALIST before taking any kind of supplements - they may interact or contraindicate with any medicines/tablets/supplements that you are already taking. (L-glutamine is also under debate as to whether it is gluten-free or not, and many low grade supplements can use wheat as a filler/bulking agent so please be careful).
Some sports drinks are laden with sugar or sweeteners (sucralose, aspartame, acesulfame K, acesulfame potassium to name a few) which have other detrimental effects on the body; do a google search and you will see for yourself, so PLEASE stay away from them - I note you say that you don't drink them.
I struggled with my weight for ages. I used to weigh myself every morning and evening too, trying to ascertain what was causing the weight fluctuations and also sometimes the stability. Do you keep a food and drink diary (time of day, type & quantity) and also track your daily weight fluctuations alongside this? You may see a pattern?
If you want any more information on anything I have mentioned, PM me
I hope this has helped.