There is no sperm in precum unless its left over from older ejaculation

Hello,

My anxiety is going off the wall.  My girlfriend recently had an issue with her insurance and for 3 weeks she has not been on her ortho tri cyclen lo.  We had sex on the 4th of January.  We used a condom which was put on prior to genital touching.  The condom did not break, slip or tear.  I checked it with water when we were done.  I also pulled out before I ejaculated.   We also had sex 3 days ago.  same story, we used a condom no break rips tears, or slips, and I pulled out before ejaculation.  Yesterday at work she suddenly threw up but said she felt ok all day today.  I'm worried of possible pregnancy.  I guess the only way that could have happened tho is precum but I've been reading there is no sperm in precum unless its left over from older ejaculation but I def. went to the bathroom before each session.   Do you guys think I have anything to worry about?