Pregnant ??

My friend had unprotected sex , on August 1st . It has been 6 weeks since her last period . She DOES have a slightly irregular period and she misses her birth control often which is probably the reasoning for her irregular period . She hasn't taken her BC since the day she had sex , and usually she starts bleeding until she gets back on track and she only bled lightly for two hours the day after the sex . She has taken 3-4 home pregnancy tests , all negative , as well as gone to our local planned parenthood and taken two tests there . One was negative , one was inconclusive . They said if she doesn't start in a week to come back . It was a week yesterday . Could she be pregnant ? If not , what could be going on ??