I don't know a huge amount about medicine, but from what I do know, as someone who's also autistic, I personally think I would probably not cope with the workload while studying or the work environment in an actual medical job. That said, that obviously doesn't mean YOU wouldn't, but I do understand your concerns. Ultimately, random strangers on the internet can't tell you whether you'll manage, but its important to be realistic about it - if your worries about this are just that, then fair enough, but if you genuinely think you wouldn't be able to cope, accepting that is important. I had a similar issue, but with college courses - I love acting, and thought about studying it at college, but, obviously, acting is well-known to be an unstable and insecure profession. In the end, I came to the slightly painful conclusion that it would not be a suitable area for me, because the instability alone would seriously worsen my anxiety. Again, please don't take this as me suggesting you shouldn't do medicine (I realise it does seem like that!) but that understanding and accepting your limits is important. Whether that means you studying medicine or not, only you can decide.
On the topic of EnviroSci, my brother, who's also autistic, is currently studying it and really really enjoys it. If you're interested in the field, I don't think it's possible you could get bored, because there's a huge variety of areas to study and potentially specialise in! One advantage (or possibly disadvantage, depending on how you look at it) is that there's apparently not really one standard curriculum for an environmental science degree, so it varies between unis. I would argue that's an advantage in that you can choose a course that focuses more on areas you're more interested in. For example, my brother is very interested in plants and forests and stuff (idk I don't study it) so he chose not ti apply for some courses that focused more on things like weather systems etc. In that way, you can almost tailor the course to your interests. Of course, if you're not interested in the area, that's that I suppose?
Have you talked to your parents, friends, teachers? They may be able to offer you some advice. My mum certainly knows my limits better than I do myself!
Sorry for the long ramble - I hope this helps a little. I'm sorry you're in such a difficult situation, but I'm sure youll figure it out!