When you consume food, the blood near your stomach absorbs nutrients and therefore the glucose levels there are higher than everywhere else until it gets pumped around your system.
So don't expect 2 different fingers to be the same unless your levels have been flat for a while.
Meter accuracy is the next thing to consider. In the UK you can expect meters to be accurate within +/- 15% which still leaves plenty of scope for variation of course.
You're doing OK. Be patient and chin up!