Late andif I had sex the night before and I took a test the next morning would it be negative

If you had sex the night before you took a pregnancy test, yes it would be negative.

So when should I take another test

If you know when your next period is due, then do a HPT four days before.

Tick

Do you know how pregnancy works? You don't have sex and then the next day boom, you're pregnant.

Here's a link that will help you understand how pregnancy happens;

http://www.google.ca/url?sa=t&source...tFBG2w&cad=rja

It's way too early for you to test. Wait until your next period is due. If you miss it than take a home pregnancy test using first morning urine.

It's really worrisome that you're having sex when you don't even know the basics about conception.