Not saying this is the absolute answer, but I run into this a lot when archers start practicing more and more without close instruction. Even find myself doing it on occasion.
#1 - If your arrows are good on the first shot and last shot, but fall lower and lower as you go it is usually a follow thru issue. It comes from reaching for the next arrow before you have completed the entire shot sequence. Three things will help you over come this: A:
shoot one arrow, retrieve and repeat. B:
If shooting a bow quiver take it off and place it on the ground behind you and to the side of your bow arm. C:
If shooting a hip/target quiver point the arrows behind you and on the side of your bow arm These steps make it difficult to get the next arrow and ensure you slow down and complete the shot sequence completely.
#2 - If your arrows tend to gradually drop combined with a tendency to go right or left it is usually creep or better termed colapse.
This is what I usually do when I start shooting a lot, but get lazy with my discipline. To remedy this I use a true tension or back tension release. But, you can address it without a $120.00 purchase by simply using Randy Ulmers "Mantra" technique. Come up with a shooting mantra that you aggressively repeat during each shooting sequence. Paying special attention to the last few steps which should include
back tension, release, follow through. Say it with such conviction that it hurts the receptors in your mind! My mantra has evolved to be simply, "I am Randy Ulmer!!!"
Sounds silly but it really does help.
You can always PM me if you are having troubles. If we walk through your steps to shooting I can often find something even if I am unable to see you. Or better yet I will give you my personal email address and you can send a video and we can go from there.
Good luck. Sorry I was late to respond. Hope this helps.
