Please can someone suggest anything else.?

i havent had my period since the 10th of oct and i have done 2 hpt and they showed up neg so i went to the doctors and i got a blood test and a wee test and they showed up neg but the doctor told me that the blood test can still show neg even if i am pregnant. i amalways tired, have a swollen abdomen, sore , and i am never late with my period i am quite the opposite i normally have it for 3 wks and then have 1 wk break and some times only a day break. i am a mother of 4 and am only 33 so to early for menopause. my husband is convinced that i am pregnant but how is a person to know if all the test came up negative. thank you for your comments and help.