What Grizz said...
And to add a bit, if you haven't been shooting all summer, (which you should be) your form will be different than last year as your muscles will have changed over a year. Your shoulders will not go to the same position, you may have gained or lost weight etc... You will shoot different in hot weather compared to cold weather due to muscle tension and the clothes you wear.
Shooting a lot in a row may not be the best plan either. Especially the first day you pick your bow up after not shooting for a long time. After a while you will start to get tired. Your muscles will act different and you will start to shoot off. And like Grizz said, it's all too easy to blame the bow. Shoot enough to learn your form. Tune your bow to your form, then shoot often enough to keep your form to the bow.
And if you can, I like to practice the one and only one shot. What I do is carry my bow out with me when I go to work everyday. Halfway to my truck I take one shot at my target. After all, 98% of the time you only get one shot at a deer, bear, moose etc. This will really teach you to make that one arrow count.
If you are hunting, practice in the clothes you wear hunting. You'd be surprised at the difference between a t-shirt and an insulated coat. Don't forget to wear your face mask if you use one. (If not, I hope you use face paint) It will change your anchor point and how you bring the string to your face without stripping it off your head. Learn to keep your form in these clothes.
And don't forget to practice out of a treestand if you use one. Same thing, learn to keep your form in the stand. Your feet will be different and the tree at your back will be different.
As for your bow, keep a journal of where things are. I have a drawing of my bow in my hunting journal and the measurements to my peep sight, nock position, rest position, sight position # of turns out, etc. If you really think your bow moved, you can check, and if required go back to your original dimensions.
Don't forget, if your bow was brand new last year, a year will change your bow. The string will creep, the limbs will set. You may have got a different release or adjusted the strap a bit.
If you want to check how your bow is shooting and would like a speel on paper test tuning, I'd be happy to run over it with you. Or just google paper testing, there's lots of good articles on it.
Practice, be consistent, learn to tune your bow, learn to stay in form. This is what makes archery so great.
As to your question for lessons, the only one I know of is Bill at Saugeen shafts in Peterborough.
www.saugeenshafts.com There used to be an archery club at the building by the fair grounds in Belleville 20 yrs ago. Not sure if it is still going or not.
Sorry for babbling, I just love this stuff. I'll resist the temptation to go on and on....