I Needed Your Help.....Ladies! Hubby & I had on 7/4/08, no sign of "aunt flo" yet. when should i test?

I don't know if I should count from the day we had or what. I'm confused about a "conception date", already took ept hpt and it was neg. How much longer should i wait? My cycle is already a week late, and having some light cramping off and on. Its uncomfortable to lay on my , and my mouth is watering alot. Ladies i'm counting on you for your advice. date is 7/23! we have a 5 year old, and i had a miscariage last nov.HELP!!!!!!!