I had a normal period Nov 16 to the 20th I was supposed to start Dec 12th but started the 13th to the 17th it was a light period. I was supposed to start again Jan 8th. I having yet and have constipation headaches acne boating back pain and nausea.I took three home pregnancy tests and a blood test all negative. Could I be pregnant and if so how far along and when did I consieve . Please help me I don't know what to do.