When can I stop stressing about head lice?

I noticed my daughters had head lice 11 days ago. I shampooed, combed, cleaned, yadda yadda yadda. Changed everyone's sheets nightly, etc. etc. I shampooed again on the 8th or 9th day after I found two teeny tiny baby lice on one of my girls. Now I'm just obsessing. Still changing the sheets nightly. Checking heads mulitple times a day. If I find anything in their hair (i.e. leaves), I can feel the panic starting. I'm forcing myself to take the sheets off the couches tonight, but I can't stop worrying. It's ruining my days!! When should I relax and go back to normal?!??