I don't know how digital tests work, so I don't know what could cause them to give a false positive - maybe the tests you had were faulty.
If you had a chemical pregnancy, you could still just have a normal/heavy period afterwards.
How long should you wait to have a blood test after a positive? I don't know. Some women never have a blood test and some women only find out they're expecting when they're far enough along in their pregnancy to have an ultrasound - so I don't think there's any rule.
I'm sorry to hear about your experience. It must have been devastating.
Rachel
http://www.fertilitystories.com