So I found out why the Analysis of Algorithms class is so hard: Math 341 used to be a requirement but was recently dropped (apparently to make things "easier").
This is the description for Math 341:
"Probability, including combinatorial methods, discrete distributions and continuous distributions using integrals. Descriptive statistics and the use of computer statistical package. Statistical inference, including confidence intervals and hypothesis testing."
So while that USED to be a prerequisite, it is no longer yet the course material is definitely still oriented towards students who have taken it.
I'm still looking for a book or something to help fill in the gaps for me, but not finding much yet...
This is the description for Math 341:
"Probability, including combinatorial methods, discrete distributions and continuous distributions using integrals. Descriptive statistics and the use of computer statistical package. Statistical inference, including confidence intervals and hypothesis testing."
So while that USED to be a prerequisite, it is no longer yet the course material is definitely still oriented towards students who have taken it.

I'm still looking for a book or something to help fill in the gaps for me, but not finding much yet...
I hope you find something to help! I was fortunate enough to know someone who had the textbook from the course I was missing.