Heya
@Alexandra100 - sounds miserable: I'm sending you much love.
How long have you been LCHF? And how long have you been under 20g carbs? Are you eating enough protein alongside your fat (too much could drop you out of Keto). It could be a simple case of having dropped too much too fast and your body isn't tolerating a drastic and sudden shift in diet.
If you've been on it a while, try increasing your salt intake and drinking lots of water
before you go to sleep in the evening (as opposed to in the morning as soon as you wake up). Also, maybe, you (delicious sounding) breakfast is just a little too much for your empty stomach to cope with, so have a little pre-breakfast, just to get it rolling before you fill it up with an entire meal. A few nuts and a bit more water or something else that's simple could help to wake your stomach up gently and, thus, avoid your nausea.
But, as
@Guzzler has noted, too, it could well be the Metformin - it's fairly common for people to find it intolerable and most of the complaints (that I've read) are gastric symptoms. If you were eating the way you are now, with 20g / carbs and the timings and amounts you've described without issue
before you started the Metformin, it might be worth having a chat with your prescribing GP / DN: Metformin has lots of different guises and types, dosages and whatnot, and it could be that you are able to identify a new version of the drug that allows you to reap the same benefits without the horrendous nausea: perhaps a slow-release, or splitting your dose so you take it twice a day... I don't know what your regime is, but there's certainly room to try other ways.
All in all, it's miserable and I fully sympathise. It's difficult to identify what could be causing it, but we can all relate to the misery your symptoms cause (and how they make sticking to your guns and keeping going increasingly challenging).
Keep posting, keep complaining, keep asking questions and looking to this lovely community for support: it's what it's here for.
Sock xx