Thick & thin yarn has bumps

It seems that the distance between the thick and thin parts of the yarn are consistent and so they come together at roughly the same spot and make a bump after a few rows. It was suggested that I knit with two balls, one on each side, but do I switch every row or every other row? How do I do every row? Thanks for your help:)

I think most folks just change balls every other row. If you are doing simple stockinette and are working (or can switch to) a circular needle and would like to change every row to see how that works out, you can… Knit a row and then slide the stitches to the other end of the circular needle instead of turning the work, join the new ball of yarn and knit another row. When you get to end of that row you turn and pick up the first yarn and purl across, then slide the stitches back to other end and using the second ball of yarn purl another row. This way you are knitting 2 rows and pulling 2 rows turning or sliding as needed to use the other ball.