Increasing Revenue for My Class Notes Site

Hey everyone!

I am currently in a computer science master's program, and I've created a website from scratch where I publish my class notes for others to read.

I've put a lot of time into it. All in all, I make very little per hour, especially compared to my day job as a software engineer. I do have the following four revenue streams:

• Digital downloads (PDF versions of my notes on a per-class basis): 57% Revenue
• Donations (Paypal): 31% Revenue
• Amazon affiliate links for textbooks: 8% Revenue
• Ads (CarbonAds): 4% Revenue

All in all, I've made ~$1650 in the past year. I've seen some 11k users, 40k sessions, and 125k pageviews, with an average session duration of of 4.5 minutes.

I'm wondering what opportunities I have to boost my revenue. I don't want to get overly "markety", but obviously more revenue is more revenue.

This is my site: https://omscs-notes.com