One of my contact lenses got lost in my eye. I rinsed my eye out and did not manage to find it. I don't know what to do. Help please?

Lost contact. Sometimes you can flip your own eyelid and the lens will pop-out. Do not keep trying to remove it as you normally remove a contact because if the contact is not present you can scratch your cornea. Lastly it is a common misconcepcion to believe that the lens can get lost behind the eye because the surface skin or conjunctiva of the eye will not allow this to happen so don't panic.
Soft or rigid lens? Can be lost under the lids (in the fornices)--if can't find it, then have an ophthalmologist look for it.
Not an emergency. I'm assuming its soft contact lenses? Its probably washed out already. However, if its still under your eyelids, its not an emergency, but it would be safer to have it removed by your eye doctor. In the meantime, just continue to use artificial tears in that eye...
May have fallen out. The majority of the time that someone comes to see me for a lost contact lens the lens has already fallen out. I think that irrigating your eye was a great idea, but if it is still bothering you see your ophthalmologist for further evaluation.
Lost contact. Often a lost soft contact lens will migrate under the upper lid. Since you have irrigated your eye, the contact may have washed out. I have also seen patient's accidentally place a new contact upon an old contact as well. If you still feel it's presence or your eye is uncomfortable, go to an ophthalmologist, who will evert or flip your lid to remove it for you.