13 lessons is good going for lateral work! (At least you weren't sat on the horse in tears!)
I would say, just relax into the saddle.. your becoming frustrated and the horse is becoming confused. Once relaxed into the saddle, lean back (sometimes we have a natural tendency to tip forward)...
Realise that you were "horse mad" and the love affair began?
For me, I am pretty sure it was my mums fault, I grew up on a smallholding and she put me on her mare before I could walk! Over the years, as my catering career progressed... I would stroke and talk to the horses on my way to work...
Lol! Im 26 and this was the day after a busy exam week at Talland and I had been pulling double shifts to get the yard done aswell as get the Estate ready (mowing, strimming, shouted at by the Huttons) :)
LOL, I threw a strop once with my instructor about Jumping and that he knew nothing! Turned out... he was an Event Rider in the Olympics and been round Badminton several times...!
My terrier would be nappy and not listen to voice commands never mind the leg, with a push I would be able to get her to cross water... I have a feeling she would just be a fat cob!
My staffie cross would walk into walls, try too hard to please and just generally stupid... its legs would be...