What Causes Low HB Count In A Blood Test?

a recent full blood count I have a HB of 104. I have no bleeding, a negative fecal occult blood, a negative colonoscopy . I am 68 and have normal healthy diet. medications I take are Zantac, omega -3, doxycycline and glucosamine. I recently had a back injury/spinal which i had Xrays etc. and required fentynal patches but have not had to use this since Dec.14. What could be the cause on low HB?. my doctor has requested more bloods for iron and another fecal occult blood test plus MSU. I worry I must have something bad like ovarian cancer