Hi Nab
Pretty much any symptom you can feel or even imagine, you can find somewhere on the internet to say that it is a sign of pregnancy!
In all likelyhood, if it is 16 days since intercourse and your tests are negative, it is *unlikely* you are pregnant. Of course you will read stories of things happening that are rather unlikely, but these are very much the exception to the rule. I know when pregnancy is the question, waiting for an answer can be torture, but trust me, the best course of action is to get off the internet and distract yourself with something else, because 99% chance you are worrying over nothing and your blood test will come back negative.
whenever you miss tablets on the pill your cycle will be out of sync so its not suprising that your period hasnt come. maybe chat to your GP about the best way to get back on track for adequate protection. and to save yourself the stress again, you might want to think about alternative forms of contraception in the meantime, and for any time that you are not confident in your pill-taking! A scare like this can sometimes be a good thing to make sure you are dilligent in the future, but it cant be much fun.

all the best!