It is possible to be bitten and feel no itching and see no welts (some people apparently do not react to bites, and others react in time--it's an allergic reaction).
If you have seen two more bugs in your apt, you have them, and need treatment. Normally I'd say get the landlord involved. If you're moving, you might need to be treated regularly until you move and then once at the new place. Lots of people who've posted here moved their bed bugs. They'd tell you it was not a waste of time or money to take every precaution.