Habe ich eine Sehschwäche mit dünnem Sehnerv?

It might be a good idea to seek medical attention since you're experiencing low fever, sore throat, etc.. Given your history of migraines, these symptoms could have various causes. If your symptoms are severe, worsening, or causing significant distress, it's advisable to seek medical help promptly.

Seeing flashes of light or "lightning" in your peripheral vision can sometimes be a symptom of an eye related issue. However, stress and anxiety can also cause visual disturbances, including perceived flashes of light. Meantime it may be helpful to practice stress management techniques, such as deep breathing exercises, mindfulness or meditation. If this also doesn't help then visit an eye specialist to get it checked.

You are experiencing an ailment called eye strain. Nowadays, it is common for people to experience problems with their eyesight. When your eyes are overworked they might be showing kaleidoscope colors or red. This is possible when the eyes are staring at light bulbs for too long. To help, rest your eyes by looking away from screens and lights. Eye drops or glasses may also be useful. 

Your eyesight has changed a bit with a measurement of -0.25D. This might make your vision less clear and give you sore eyes or a headache. If you spend lots of time looking at screens (like phones), these symptoms could get worse than they already are. To protect your sight, attempt to keep screen use down to 2 hours everyday maximum and take breaks every 20 minutes or so where you focus on something in the distance. You should still wear your glasses as directed by the optician as well.