IMO, flea collars are a waste of money, and I don't think any of the over the counter products are worth anything more than free.
You're not going to get ahead of this without using an effective product.
Ask your vet what they recommend, here in the South, we deal with this multiple times a day.
Ivermectin has no effect on fleas, and I definitely recommend not using large animal ivermectin on your pets.
Sophotrol is a good product. The permethrins work quickly, but break down rapidly, which is good. You don't want things that will accumulate in the environment, the way DDT did.
The IGR (insect growth regulator) does not kill fleas or any other insect. It inhibits the formation of chitin, which forms the flea exoskeleton and the shell of the flea eggs. If you've ever eaten shrimp or lobster, you've been familiar with chitin.
The problem here isn't the eggs, it's the pupae. Fleas form cocoons like many insects. There is nothing you can use except for perhaps the steam cleaner that will kill them in the cocoon.
I often recommend vacuuming daily. Studies show that a vacuum cleaner will kill 100% of the flea eggs and larvae that it picks up, and 96% of the adults. Again, no effect on the pupae, they are down in the carpet where nothing will affect them.
When an adult flea pupates, it's protected by the cocoon. One it emerges, it's ready to feed. It can go up to a year without a meal at this stage. Once it feeds, the gut becomes activated and then it becomes what we call an obligate parasite. It can't go more than a few hours without feeding.
One female flea will lay her own weight in eggs every day, or about 500 total eggs in her lifetime. It's no wonder that an infestation can get so bad. The signs are often there long before they are recognized, but then it's really a nightmare.
Situations like this are why I recommend continuously using an effective product. Skipping doses just makes the fleas resistant. When Frontline and Advantage were first released, they worked amazingly well. At least here in Florida now, they're useless. I don't know if flea collars ever worked, certainly not in my lifetime.
It's a lot easier to keep them out then try to get them out.