I'm sorry you have lupus, on top of MG. And you think you needed to be well-educated about MG!
Lupus can be a bit more complicated. Here are some of the Florida sites for Lupus. There's the main Lupus Foundation site (national), a local group that splintered off and another group I'm not so familiar with.
Is the "other drug" that may make MG worse Plaquenil? Some people with MG can take it.
There is also an over-the-counter supplement; a natural anti-inflammatory that you can bring up with your rheumatologist:
It is invaluable to try to make it to some Lupus support groups in your area. There's nothing like the firsthand experience from someone else with lupus.
I suppose you know to stay the heck out of the sun. It can flare lupus quickly. Even sun that comes into a car while you are driving! Because of that, you need to take extra vitamin D along with calcium (more than most people take). And some people get their windows tinted to keep some of the harmful rays out.
Did your doctor, or primary doctor, check your baseline kidney function? Do a UA to look for protein? If not, that's something that needs to be done regularly, even if you don't have symptoms. Your primary doctor can work with your rheumatologist (or not).
The MOST important thing with lupus is to bring up any new symptom to your doctor right away.
Pampering your immune system will help. Sleeping more when you feel worse, eating good foods, etc. I'm sure you already know this stuff but I had to put it out here anyway.
Lupus is different for everyone. I've known people who do okay and, yes, there are some who die from it. You should be aware of all the possibilities so that you will be proactive about your health as much as possible.
I'm sorry you have to deal with this. I hope you have a good support system and family to help you. Give this some time to sink in. It's a lot to think about.