Another thing, worrying about it can delay your period too. That's happenned to me before. Easier said than done, but try to relax. Well, a pregnancy test wouldn't show positive until the first day of a missed period. If you get a blood hcg from your doctors it could be as soon as 10 days, but even that is too soon also.
Some women are really fertile though and can get pg anytime of the month.
If your cycles are 35 days long, then you probably ovulated on day 21. If you have any questions, please email me. Another thing, worrying about it can delay your period too. That's happenned to me before. Easier said than done, but try to relax.