Memory Allocation Problems

My site keeps on going down because of memory allocation problems and I cannot figure out how to stop the processes from starting up. I have had lots of correspondence with the hosting service and they say that processes have started and they are eating all the memory. I cannot figure out why they are starting and only the hosting service can stop them. Do you have any recommendations? The error message reads: Fatal error: Out of memory (allocated 3407872) (tried to allocate 115708 bytes) in /home/segullah/public_html/wp-includes/wp-db.php on line 1780.

The line changes and the file changes as you try to access the site.

Things I have tried:
1. getting rid of any unneccessary plugin
2. allocating more memory in the wp-config.php file.
3. talking to the hosting.