Is she saying that she thinks this is a life-long condition for you?
Oxford criteria says "definite onset of symptoms, not life-long."
It can still be gradual onset. Is it possible that your doctor has misunderstood? I've not heard of people failing to fulfil Oxford criteria in this way before.
Also, I'd have thought that GPs would tend to use the NICE critieria, not Oxford. This is the NICE criteria:
Healthcare professionals should consider the possibility of CFS/ME if a person has:
fatigue with all of the following features:
new or had a specific onset (that is, it is not lifelong)
persistent and/or recurrent
unexplained by other conditions
has resulted in a substantial reduction in activity level
characterised by post-exertional malaise and/or fatigue (typically delayed, for example by at least 24 hours, with slow recovery over several days)
and
one or more of the following symptoms:
difficulty with sleeping, such as insomnia, hypersomnia, unrefreshing sleep, a disturbed sleep–wake cycle
muscle and/or joint pain that is multi-site and without evidence of inflammation
headaches
painful lymph nodes without pathological enlargement
sore throat
cognitive dysfunction, such as difficulty thinking, inability to concentrate, impairment of short-term memory, and difficulties with word-finding, planning/organising thoughts and information processing
physical or mental exertion makes symptoms worse
general malaise or ‘flu-like’ symptoms
dizziness and/or nausea
palpitations in the absence of identified cardiac pathology