Wondering...please help

How many weeks along do pregnant tests stop working/picking up HCG levels.??? If that makes sense? I took a pregnancy test after 7 weeks of unprotected sex because I got my period 4 weeks after he put it in for a couple of seconds with little to no precum...but I still felt like the need to take it to ease my mind. and it came out negative. Is it an invalid or accurate? Also I've been having clear discharge since last Monday and it feels like my period usually does?? Am i okay? Does this mean AF is coming soon? Ugh I hope so. Please help me out, thank you so so much.