I had protective sex, used a condom 2 weeks ago it has been 18 days 3 days late and took a pregnancy test the day i was suppose to get it the day before and yesterday and they all came back negative should i be worried if i used a condom???

Three negative pregnancy tests after 18 days makes pregnancy unlikely. That said, condoms are not 100% effective, and neither are home pregnancy tests. If you don't get your period soon, you will have to keep testing, or see your doctor for a more precise test.

Conception occurs within day or so of the sex. It takes about 3 weeks for the embryo to make enough HCG for a positive pregnancy test. Blood test may be done a day after a missed period. Home pregnancy tests should be done 4-5 days after the missed period. If the result is negative repeat the test in 4-5 days. Use first morning urine and follow instructions for the test carefully.