Kevin is correct on the riding part.....you need to get assistance from a trainer/instructor before you and your horse get hurt.
As far as the horse being cinchy, many horses get uncomfortable when you tighten a cinch. It's not necessarily about being pinched (although an ill-fitting saddle can lead to cinchy behavior), but it's often about the confinement of having something strapped around your stomach and tightened. It's like someone tightening a belt around your waist. Make sure you are tightening your cinch slowly and in stages. When you first put the saddle on, tighten the cinch slowly and only enough to keep it from falling off. Walk away and let your horse get used to it. Come back and tighten it a couple of inches then walk away. You might have to tighted 4 or 5 times before you ride, but take your time. I have gelding who has been cinchy ever since I bought him. He has never tried to bite me, but he bites at the air. I take it slow and easy on him and he has improved considerably.