No no no, you actually want to clean all the silicone out of your hair one last time using sulfates so that you don't end up with the same problem! So don't worry about making your shampoo sulfate free this one final time.
If I were you, I'd either check your old stuff or go into the sample aisle of the drugstore, where they sell the little bitty bottles of shampoos and stuff, and look for a shampoo that has sodium laurel/laureth sulfate as one of the very top ingredients but DOES NOT contain any of the silicones everyone else mentioned to avoid above. Use it tonight or tomorrow and then never again! That way, you'll have a clean slate, and as long as you stick with the products listed above, you should be okay!