Hello from Poland. Lots of sysadmin experience here. I can help you but this has to cost a little more than you propose because it is a time consuming thing. I will need to carefully audit your system and the website as well. There are too many reasons for such behavior to list. I do solid work. Please see my profile for some references. Thank you.
Hello,
I can help you analyze, check and optimize your site. Also, I can provide you with security tips and tips on how to keep your site fast.
Best Regards,
Aleksandar.