Here is an explanation of the serum iron test:
Serum iron is a measure of circulating iron bound to transferrin and reflects total body iron. Serum iron measurements may be affected by menstrual cycle, time of day, diet, hepatitis, and use of iron containing placebos found in some oral contraceptive packages. On its own this test just gives a snap shot in time of your iron levels and it is not very helpful for defining a chronic iron deficiency or other iron problems. However, when the test value is examined in comparison to other iron tests it can help provide information leading to a disease diagnosis.
Ferritin is the storage protein that holds iron for future use. It is generally the test that shows whether or not you need to suppliment iron (optimal levels are 70-90). However, there is a disease called hemochromatosis where ferritin levels can be in "normal range" but serum iron levels are high and you should get some follow up testing to rule it out, specifically a transferrin saturation test. I would also retest your serum iron levels and make sure the testing is accurate.