Why would my dilantin level always be low no matter what dose i take it has been 2.1 to 3, 1 for 16 years and im seizure free only had one in my life?

Low dilantin level: I assume u take med regularly. Many meds & supplements can interfere with dilantin: antacids, aspirin, tylenol (acetaminophen) (also in combo with narcotic), gingko, milk thistle, contraceptives, immune modulators (for ra/ ms/autoimmune dss), HIV drugs, calcium channel blockers, tagamet, cipro, erythromycins, valium, diabetes meds, flu vaccine. Discuss possibilities with prescribing doc. Good that no seizures.