Why is my in ear measurement different to other areas?

It is normal for temperature readings to differ per measurement method and measurement site. Normal oral, rectal, in-ear and axillary body temperatures are below:

ADULT Men:
Oral: 35.7-37.7 °C (96.3-99.9 °F)
Rectal: 36.7-37.5 °C (98.1-99.5 °F)
In-ear: 35.5-37.5 °C (95.9-99.5 °F)

ADULT Women:
Oral: 33.2-38.1 °C (91.8-100.6 °F)
Rectal: 36.8-37.1 °C (98.2-98.8 °F)
In-ear: 35.7-37.5 °C (96.3-99.5 °F)
ADULT Men and Women:
Axillary: 35.5-37.0 °C (95.9-98.6 °F)

Source: M. Sund-Levander, C. Forsberg, L.K. Wahren. Normal oral, rectal, tympanic and axillary body temperature in adult men and women: a systematic literature review. Scand J Caring Sci; 2002; 16; 122 ;128.