Dog Allergies Treatment

I gave my cat and dog sentenal for 4 years, There last pill was given Nov 1. They have been scratching for 2 months and the vet said they had allergies. On Sunday I discovered my dog has a tapeworm that you can only get from fleas. Two hundred dollars later they are both on deworming medicine and advantage to fight fleas. Although I don’t see any fleas, and no one is being bit by the fleas accept the pets, I know my home is infested because both pets have them. What are some of the best methods for getting rid of fleas in my carpets and beds and sofas . Do I need to worry about solid surfaces and how do I know when the are gone? I don’t want my pets infested again. What was the point in giving them the sentenal I wonder?