According to the local MLS rules, Realtors must put a listing in the MLS within 5 days of signing the listing agreement. So if you just signed it, your agent hasn't entered it yet. Check with him/her.
When did you put it on market and which website did your agent subscribe to? Listings may or may automatically come on Trulia depending on if your agent;s office or any site he advertise your property syndicates to Trulia. It might take a few days to show up, depending on the frequency those sites feed into Trulia. .