If a pregnancy test is positive, it's nearly ALWAYS positive. However negatives can be wrong sometimes (this is what I was told by a pregnancy test manufacturer's helpline once).
The "side effects" of pregnancy shouldn't have kicked in yet (ie nausea, tiredness etc) as you would only be 5 days pregnant. However, it does sound like you could be.
The only way to tell for sure is to get a simple blood test taken by your doctor. Then you'll know for sure. You should also speak to your boyfriend about how to use birth control (and STD protection) correctly. The condom has to stay on ALL THE TIME until he withdraws.
Good luck.