First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes. The symptoms and history that you describe are consistent with compressive injury of the peroneal nerve at the fibular head (the nerve is pressed against the small bone on the outside of your leg just below the knee). These injuries can be mild and only cause conduction block/demyelination (loss of insulation around the wires-making the signals flow slower) or more severe with the loss of "wires". Mild injuries improve with in a few weeks to 3 months, while more severe injuries will take 6 months or longer. If you have an injury that involves axonal loss (loss of wires) than atrophy can occur in muscles below the lesion (the tibialis anterior (shin bone muscle)). From the story you describe, I would not expect thigh/buttock atrophy, unless the compression was higher.
ALS is a progressive disease caused by loss of the motor neurons that control muscles. It can present with foot drop, muscle atrophy and weakness. However, ALS does not get better. Thus it is very unlikely that your foot drop at least was a manifestation of ALS.
I think your risk of ALS is low, but due to the seriousness of ALS, I would make sure you get an extensive EMG (needle exam, not just nerve conductions) to evaluate for ALS and the cause of your atrophy. I would also recommend an MRI of your spine. There are also some genetic conditions that can predispose people to pressure palsies such as HNPP (Hereditary Neuropathy with Liability to Pressure Palsies) and can be tested for at the discression of your neurologist.
I hope this has been helpful.
My question is this: If a mild injury lasts from weeks to three months (approximately), will I continue to feel the pain and require pain medications for this period, as well? I've been told that sensory and motor injuries to the nerve are atypical and no one has been able to give me a definitive answer. Is the resolution of this type of pain difficult to predict?