Birth control pill ineffective?

Hello there! I take my yasmin 2 pills regularly and have had no problems so far. The past two days though, I have had the stomach flu. Yesterday I had the runs (TMI, sorry!) twice, and today once, although they were both like 11 hours after I took the pill. Will that render them ineffective? Will I have to use a back up method for a week, or the rest of my cycle or what? Unfortunately I'm allergic to latex so I really hope thats not the case!