It looks to me like you are attempting to quilt fairly close to your seams and stitching through your seam allowance. This makes it harder as you are going through all those extra layers. I use 1/4" painters tape and place it right next to the seam and quilt right next to the tape. I am then far enough away from where I pressed my seam allowances and I have nice straight lines of quilting that is evenly spaced away from the seam.
You can also measure with your cutting ruler and draw a chalk line or use a sliver of white soap on your dark colors.
I do not use a thimble either. I push the needle with my fingernail. I use my index fingernail when quilting towards me and my thumbnail when quilting away from me. I am side to side quilting challenged and prefer not to quilt going left to right but rather up and down. I use a lap hoop so I can turn the quilt in the direction that is easiest for me.
What size needle are you using? The smaller the needle (which means a higher number, a size 11 is much smaller than a size 8 with needles), the smaller the stitches but it takes practice and experience to feel comfortable with size 10 or smaller.
Are you using any kind of hoop or frame? How tight is the quilt in it? You want it kind of loose so the fabric has give when you get into the rocking motion of the needle.