Does cephalexin affect sprintec birth control pills?

No: There is no direct negative interaction.

No risk, no worry: It's an outdated urban myth that antibiotics interfere with effectiveness of birth control pills. They do not, except occasionally with rifampin, an infrequently used antibiotic for certain infections like tuberculosis. Lamisil (terbinafine) certainly has no effect. See https://www.drugs.com/article/antibiotics-and-birth-control.html