Recently I cracked open Principle of Analysis by Rudin. I got stuck pretty much straight away and looked it up - I saw a few suggestions for a bridge between high school maths and the rigor required by that book. I'm now reading another book that took inspiration from the previously mentioned book but gives a bit shallower a slope towards the rigor required.
https://www.reddit.com/r/math/comments/50m4ib/what_are_the_m...
https://www.reddit.com/r/math/comments/4jopme/is_it_prematur...
https://www.reddit.com/r/math/comments/512p2p/analysis_text_...
I find getting a taste and moving forward breadth-first keeps things fresh.
Try different media. I've found, at least for me, sometimes just reading it won't click. I pull up some ocw or a random video on youtube and presto. It is important to remember that when it clicks that what you've been reading makes sense and to reread. Sometimes I'll go through like 5/6 videos, it is just finding the right one.
Try problems. Struggling is the key to success in mathematics. There is no doubt in my mind that this is true.
If you REALLY have problems look up a professor at a local university or community college. Find out when their office hours are and send a polite email asking that if they have time you'd appreciate the help. This will be hit or miss, but many are glad to help (no one does academics for the money). Many will even let you sit in on their classes (less will grade your work).
True, but the fly-in-the-ointment here is that sometimes notation changes over the years, and comparing papers / textbooks across textbooks can add even more cognitive overhead in that sense. :-(
... comparing papers / textbooks across decades can add even ...
Plus, there are enough old math books (out of copyright) to just include scans directly. I actually collect math books, have a few infitesimal calculus books even.
Unless you can afford a tutor to teach it several different ways until it clicks, which is functionally similar.