"He's failing at the best thing I excel at, which is science, with a D+. I don't know what assignments are due or when they are due because he is expected to write them down in his agenda. I just emailed the principal and teacher with a request to meet for a parent teacher/principal conference."
Question: is he failing due to not applying himself, or is he genuinely struggling with the subject? Yelling won't help, and he will learn to tune you out. I know you are already busy, but you may want to read a bit about performance management. It's something I learned regarding how to reinforce desired behavior and extinguish undesired behavior in the workplace, and I brought it home and used it with my children. In a nutshell, you apply consistent consequences for behavior, reward the good with positive reinforcement, and try to extinguish the bad with negative reinforcement.
So he loves to play Fortnite. I recommend not deleting it just yet. You said you only let him play on weekends. How about changing tactics, and allowing him to play it for a certain amount of time on weeknights once he completes his homework? Bring home a bad grade on a test, Fortnight goes away completely for X number of weeks. Earn it back by making a good grade on the next test. Let him understand that his own actions drive his consequences, and mom stops yelling.
Motherhood is difficult, being a nurse is difficult, school is difficult, and marriage is difficult. Mr. needs to understand you need his help and support. I hope you can make him see the light.
Hang in there!