Benoit is absolutely right,unfortunately you are forcing your hand into unfamiliar positions - mine used to hurt so much i ran then under warm water and stretched them phsically - it hurt 'cos that was almost 20 yrs ago and i can still remember the pain. Hang on in there and try playing for short periods first then lengthen your practice time.
Re: "if your arm length is this and finger length this we recomend you start with this size guitar".(etc)
No, most people get a guitar by trying several and seeing which fits- BUT, there are two scale lengths (commonly!) Fender, which is 25.5" (648mm) and Gibson 24.75" (628mm) and you may find it's easier playing a Gibson scale length neck as the strings are less taut and take less pressure to fret- but then "feel" varies greatly with individual types as a couple of my fender copies feel easier to play than my gibson copy.
Numerous factors such as "height"/depth of neck [ie what size it is at a certain fret,say 22mm at fret 12 for example] and width of neck come into play here,as ddo string thickness etc,etc,etc.
-may ilustrate my ramblings better than i.
Fender used to make student models which had short scales and were easier for learning on - hence student- You may want to try looking for a Fender Bullet to play,
- Sorry i don't know Ovation's usual scale, but acoustic guitars are harder to play at first , because acoustics usually have thicker strings than electrics.
Ask a guitar teacher or friend if you can borrow theirs or go back to the store and play about with some electrics (strats,teles,les pauls and sgs) to get an idea what they are like.
I only found out about different scale lengths a while back and found it makes a lot of difference.
Fight back and buy a slide for when the fingers get tired