Math, accounting, and economics the same semester would require a lot more study time than some other combination. Teaching certification courses are blocked - certain courses need to be taken during the same semester. Take at least 16 credits each semester - at a minimum, you need 128 credits to graduate. If you want to complete your degree in 4 years you need to average 16 credits per semester. All courses are not offered every semester, they follow a rotation.
Some courses only have one section.
They are typically offered the same times and days each semester they are offered. If two classes you want conflict in time, one will have to wait until another semester. Put your difficult classes on a MWF schedule if possible. That allows for smaller doses with more repetition. Recognize when your energy peeks are.