stretchy clear discharge means that you are ovulating
you do not ovulate when you are pregnant
if you was being sick 3 weeks ago and your not due your period till the 21st, that means you have had a period since you have been being sick
the earliest you can take a test is 2 weeks after you have had sex (even then its not very accurate) but it doesnt sound like your pregnant
you have to wait until your period is 3-7 days late then take an hpt. if you take it too early it won't detect the hcg in your urine.