I was prescribed one dose, 4 pills of flagyl for trich. i took 2 pills and five days later took the other 2. is it still effective?

Not reliable: Why didn't you take the full dose as prescribed? There's no research on treatment with 1 g of metronidazole (Flagyl®) taken 5 days apart. Most likely it would work, but no way to be sure. Speak with the doctor or clinic where it was prescribed. Probably they will recommend re-treatment with the proper dose. Or maybe re-test in 2-3 weeks with the newer DNA test (not microscopy or culture).