As trophywrench says, get professional guidance. I'm wondering though if there might be ways for both you and your employer to make reasonable accommodations for each other. So there's an issue with you carrying drinks and sweets on site. There might be many reasons for this this, don't feel you have to explain them. But what about glucose tablets, as Tina suggests?
As you say, you are self-medicating. Sweets and drinks, however, are also just general foodstuffs. It may be a case your manager is being petty, or maybe other workers are raising objections because they don't see why you're allowed to carry jelly babies around with you when they can't. Glucose tablets are much more clearly 'medicinal', not to mention more compact. If the issue here isn't something to do with hygiene, then it might be that you can make the case to your employer that you should be permitted to carry glucose tablets with you and use those as an immediate fix, and then return to the restroom temporarily should you really, really need to. This way you'd have the security of glucose on you in case you have a hypo, you've shown that your diabetes is something that can be easily worked around rather than being a pain for you or your employer, and you've put forward a suggestion that actually boosts your productivity.