For the vomitting id say u drank to much. U cant compare before sex not vomitting to after sex since alcohol makes u sick when u drink to much or a certain kind(this coming from a girl who has hugged the rim plenty of times) as for being pregnant the precum has sperm in it and sometimes faulty condoms happen (i have a baby sister thanx to durex) but I would bet unless hes got strong swimmers and u are extremely fertile than u probably arent. But in the case that u are sharp pains are not normal and could be signs of an eptopic pregnancy that requires surgery to remove and since they can be very dangerous cause u infertility, damage to your fallopian tube and possible death u should seek medical attention. It is possible for a pee test to be negative if you have an eptopic pregnancy.
I think sharp pains an late period would be enough to send me to the er just to b cautious

How late is your period? Perhaps stress is throwing it off by a few days (it would only be a few days though). Dunno what else to tell you. The best advice that I can give is to get on a hormonal bc after this scare is over, it's much more reliable than condoms.