Pregnant??? need a little hlp?

i have been off bc for about a month now. my period came on on the 17th of this month. I had unprotected on the 21st, 22nd, 24th,and the 25th. i've been having back pains, horrible stomach pains,diarrhea,nausea,mood swings(and almost everything has been getting on my nerves) and also slight headaches. could i or do u think im pregnant? ( i took a pregnancy test on monday it came up negative but i was thinking it was probably just too early to take it) please help and explain... when should i re-take the pregnancy test ??