Periods are missing. Negative everyday?

Hello , my girlfriends period cycle starts 27th to 29th of next month ( feb 27 to march 28) and we had unprotected sex on 5th day of her period i.e., on march 30 and she took contraceptive pill within 24 hours. After 14 days she had mid cycle spotting for nearly 4 days ( thick red spotting on 14th april ) and later that month the period occured late on may 3. ( 4 days late ) so she did HCG test for 4 days and its showed negative (control). Why she had 2 periods in 1 month ? And Now the problem is today is june 9( 5 days from normal period time) but she did not get her period but getting witesh fluid with very bad smell :( :( :( we are worried and she has been doing HCG test everyday from past 4 days its showing control ( negative) . I would like to know why its happening ? Why she missed her period ? Will it come or not ? Is this common if it its why ? Is she may be pregnant ? If she, why is HCG is showing negative everyday ? What should i do now please clarify me. Thank you.