Hi. So, you are likely not pregnant. First, he had on a condom and the fail rate you read about condoms happens when they break. This condom was intact and you'd know as when a condom breaks, it's a big old mess. Second, you followed up with good measure with Plan B. That works very well when taken within 3 days of the sexual episode. But the way it works is that it is a big dose of hormones. Big does. And this upsets things so you can't conceive. However, those hormones also are still in your system and have to work their way back to normal. And, therefore, most women are irregular for 2 to 3 months after taking Plan B. That you are late is not at all unusual. By the way, things like nausea are not common super early in pregnancy. They happen about week 6 to 7 in pregnancy.
You can always take a test and a simple pee test you buy at the drug or grocery store is great to be sure. You can do that from 2.5 weeks after intercourse and on. So, can do it now. But I really would fall out of my chair if you were pregnant. I just don't think you had much chance of that happening. good luck