When I used frontline plus, the direction says to apply once a month for 3 consecutive months...then just for fleas, re-apply every 3 months. For ticks, re-pply once a month. Frontline Plus always worked for us, but for some people in other states, it wasn't working...something about the fleas growing immune to the Fipronil, the active ingred in frontline.
Hope you'll find something that works...they hide inside the carpets, cracks & crevices.