It sounds to me you are forgetting to pull bottom thread to top then holding these threads as you start off. ( when I forget to do this I always get bunching on the back. Later sew these threads in.)
you need to do a practice of walking foot with thread tensions on a small sandwich before on the main quilt. Take note or 'photo of settings then change to do your quilting.

For newbies, I always suggest you use the same thread color in the bobbin and the top thread. It takes time to learn how to correctly adjust your tension. I usually quilt with the length of 3 and it is a good idea to replace your needle when starting a new project. I found it helpful to take a class at my LQS 20 years ago from Harriet Hargrave. I own her book which is my primary go to book in my library. She has come out with her 4th edition:
http://www.harriethargrave.com/Books...ition-p79.html

usually use the same color on top and bottom or at least as close to the same. I would take out the bobbin and rethread everything. Well if the loops are on the bottom it is the top tension. Check your bobbin tension

Usually thread bunching is caused by the thread coming out of the take up lever.....rethread, use a 90/14 topstitch needle.....if you take off the walking foot, put a quilt sandwich in the machine, sew straight stitches....and your tension is ok...Don't mess with your tension. Always check your thread weight to your needle size..normally 90/14 topstitch, lengthen your stitch slightly, pull up your bobbin thread to the top before you start to stitch. Let us know how things work out...