Usually when you have a kidney infection you have fever (can be quite high), pain in the "loin" (lower part of back and sides between the ribs and pelvis). If you tap on that area with your fist it causes excruciating pain - makes you flinch.
You can see traces of blood in your urine. Your urine can become cloudy, smell aweful, and you can have increased frequency (pee small amounts much more often).
Nausea and vomiting is usually a common symptom. But pain can also cause nausea.
In terms of how sudden it comes on, everybody is different but it generally comes on gradually (depending on where the infection comes from).
A muscle strain in the back can cause pain. It usually comes on suddenly after something like picking up a heavy object (you can pull a muscle without knowing though). Pain meds like Tylenol would help with the pain, along with heat pads or "topical" medication like Ben-gay. It usually disappears after 2-3 days.
If you wanna wait it out for 2-3 days it's your decision, but if you have the above symptoms, it's more likely that you have an infection. It can be quite serious if not treated though.
Your hubby is correct. Your health, comfort, and especially your kidneys are more important than money.
All the best.