Ok,
Having the same issue, it is a hosting issue, If your database + plugins are larger than what your hosting provider can provide there is nothing they or you can do. I have rebuilt my website to get ride of all the junk in the database and I only use the plug ins that are necessary. But typical memory that hosting providers give is 30mb. I am with 1and1 and they just upgraded to 60 mb memory so that is how I got it fixed.