Monitorix might come in handy here. It does not exactly focus on Apache, but of course includes Apache-specific data:
Monitorix: Apache Statistics (source: Monitorix.Org; click image for larger variant)
As the graph shows, you can easily see a "journal" of Apache resource usage: idle/busy workers, requests, CPU-usage. Together with plenty of other statistics (see here for more screenshots; there can be other reasons for your "slow loading times", e.g. another process hogging all resources), this gives a pretty good image on your server's performance. Statistics are saved using RRDTool, and the web front-end allows you to select different intervals to view the stored data.
Monitorix is available for download for multiple systems, and easily installed on most Linux distros directly via their package management (APT on Debian and its derivates, RPM for RedHat/Mandriva/SuSE etc). For more details, please also see my answer here.
I'm using Monitorix on multiple servers, and it saved my day more than once. The dev is quite busy implementing new features, and support is great also on its IRC channel in case you need help quickly.
Disclosure: I'm the maintainer for the Monitorix Debian/Ubuntu packages and the corresponding repository.