First trimester (Extreme Morning Sickness)

Good morning everyone! For context, i am currently 7 weeks pregnant and I have worked at my job for about 4-5 months, have started receiving health benefits and I feel pretty set in my path at the moment, then about a month ago I found out I am pregnant and it’s caused a lot of attendance issues as I have extreme morning sickness to the point where I cannot keep anything down most days of the week, and have to take the medication prescribed by the doctor I saw at the ER. Recently my employer was trying to fire me over leaving at a set time. (7am) We come in at 2:30am and leave when the workload is done. Anywhere from 7:30 to 9am. He said it was too early in the day, and a problem for them (even though plenty of people have set times they leave). I felt it was an excuse to cut down on their staff that was hired for the holiday season, So I had to explain I am pregnant and have a hard time staying there for long periods of time, it is a warehouse type of job, its extremely loud, not the safest and with my nausea and vomiting its overwhelming. They seemed to back down when I finally brought up my pregnancy, but without my first doctors appointment, (I’ve only been to the ER so far for throwing up badly 3 days straight) I feel I have no evidence to prove myself if I have to make callouts. Should I get a note from my doctor on my first appointment on Wednesday to give to my job? Or is it inevitable that they can fire me over attendance anyways?