I've recently received a bunch of questions about diabetes and related conditions, and decided to respond to some of them here.
Caffeine has long been suspected of having some deleterious effects on diabetes, mostly on type 2 diabetes. For instance, one study showed that pure caffeine given to coffee-drinking adults with T2D raised both glucose and insulin levels somewhat, compared to placebo. But caffeine is rarely consumed alone -- it's usually consumed in coffee or other foods that contain additional compounds that might either augment or offset the effects of the caffeine. One researcher summarized the effects of caffeine in his comment: "For people with diabetes, drinking coffee or consuming caffeine in other beverages may make it harder for them to control their glucose."
Color changes and swelling of the feet indicate that the blood supply to the limb is impaired. This could be due to partial blockage of blood vessels, either in the foot, or perhaps as high as in the groin. Surgical repair of the blockage might be needed, but the first step is to get simple studies such as Doppler ultrasound of the legs to look for impaired blood flow.
The numb sensation of your feet and hands implies a different problem called peripheral neuropathy that frequently coexists with impaired blood supply in people with diabetes. Discuss with your physician, and arrange to get testing done!
All approved sweeteners are fine for folks with diabetes. Some of these are artificial, such as aspartame, sucralose, acesulfame, and saccharin, while others are "natural", such as stevia. "Coconut sugar" has been promoted as a sugar alternative, but it still contains calories. I'm not aware of any evidence that folks who have pre-diabetes should or should not use it, but if you do, use it sparingly.
A value of 68 mg/dL (3.8 mmol/L) is slightly below the usually expected range, which most authorities describe as going down to 70 mg/dL (3.9 mmol/L). What to do? First, if it was unexpected, recheck the value -- meters are not terribly accurate and the repeat value might be higher or lower. Second, if it's confirmed by appropriate symptoms or repeat testing, eat some carbohydrate ASAP. Examples of appropriate carb choices would include apple or other fruit juice, sugar containing beverages (including milk!), glucose tablets, or other foods that are high in carb such as cookies. See Hypoglycemia for more information. Third, figure out why you went low -- if you can't identify why, talk with your physician or diabetes nurse educator to get their help to identify the cause.
You describe several health issues that you are trying to cope with, and the combination makes it very difficult to give any specific advice over the Internet. If you haven't discussed your hip pain with your physician, and had an evaluation by an orthopedic surgeon, you should do so. If you are already seeing an orthopedic surgeon and the recommendations of the specialist aren't helping, you will need more testing and/or a second opinion from another specialist.
I have no idea why you were told you weren't allowed to have snacks. I'd strongly urge you (or the cook in the family if you're not doing the cooking) to consult with a diabetes dietitian, preferably one who has the CDE credentials. If your present medical team doesn't include one, you can search on-line for one.