Check your Magento version, upgrade that to the latest stable version
let me know if this works for you.
Many have contributed to this thread; however, there is a lot of information posted that will steer you in the wrong direction. Keep in mind many posters here are attempting to sell you something, looking for work, or have no real practical real life experience working with Magento day in and day out for years. If they were busy, they wouldn't have time to post ;-)
That said, AWS servers are NOT slow. T3 class servers are fine and world class! [No concerns over CPU credits.] We have very large customers running < 1.5 secs on t3-med to t3-xlarge with some customers with well over 2k unique visitors per day at less than 10 ~ 20% utilization.
One customer is running a t3-medium, and has 1 Million SKUs and 3K categories. Yes! That is NOT a typo. The performance is amazing!
Additionally, if you want to run with Elasticsearch disabled for 2.4.x+, we have a solution. This will also speed up performance. [DM for more info]