If your bobbin thread pulls out without any resistance, then it is the upper tension. When I get loops on the back, I find my upper thread is feeding too fast. I run my upper thread thru my bobbin winding hook. Do you have one on top of the machine?
Also: your thread. Thread that is wound on the spool like the old fashioned thread should stand on an upright spindle. If it is wound by crossing the threads around the spool, it should be layed on its side. Could this be the problem? Suz