Dec 24 my last period, feb 1 i tested (-) 4 pregnancy but up 2 now no period wat wud i do next?

My last period was dec 24, my husband used condom for 3 weeks and i should have my period jan 24 to 28 but it did not come, last feb 1 i used a home pregnancy test and it was negative, i'm a little worried bec up to now i still don't have my period. we have 2 girls (2 yrs old and 11 mos old) via CS and i can't afford to have another one. please help!!!!