We get this question quite often. Fleas, bed bugs, Springtails, Mites and almost any insect that could be causing this issue are very visible. So if the itching is not caused by a visible insect, that means the problem is caused by something that is smaller or could even be unrelated. Anything smaller than an insect is either bacteria, allergens, pollens, etc. These irritants are not killed by pesticides. So spraying for something you can't see is useless. If you can see what is biting you, then pesticides are an option. If you can't find whats biting you, then pesticides are useless and can be even be harmful when overapplied and misused.
We have a great page here - http://www.epestsupply.com/bugs-insec...
Hope this helps.