Real Estate problems...?

I have just bought a home. We closed on the 29th of Feburary. Once we moved in we realized the plumbing was bad. When the upstairs toliet is flushed, I get sewer water coming up in kitchen sink & threw the laundry drain. The seller did not disclose this, nor was it in the inspection. Can I sue to get the problem fixed, or is it all on me? THis was an FHA Loan, & it was not a AS IS Home. My home owners Insurance says it was pre-exhisting & they can't pay for it. I had 2 plumbers come out, & say that I have severly deteriorated pipes under my slab. Which is affecting my foundation. Cost of repair is anywhere between $7000-$9000 depending on what more they find after they jackhammered up my home. I live in the Dallas fort worth area.