I apologize you are having this experience with working in your account! Are you seeing any error messages? You mentioned this continued to happen after clearing your cache and reloading our site in the same browser. Are you having this experience when using a different browser? Or even opening your account in a private/incognito window? If you have not yet tested your browser this way I would suggest doing so. It allows us to see if there are any 3rd party add-ons that could affect how Constant Contact works.
Would you be able to provide some of the following info so we could investigate a bit more?
1) Does using another browser, such as Firefox or Safari, load the website faster?
2) What is your ISP (e.g. Comcast Xfinity, Mediacom, Verizon, etc.)?
3) Could you please run a speed test via fast.com and let us know what it says for Latency and Upload in the Show More Info area after completion?