CanoePam

If an issue shows on the bottom, the problem is in the top. Recheck the threading, make sure foot is up while rethreading, and use a new needle.

Jordan

It possibly could be your bottom tension -or-you might want to check how your bobbin goes in. On my Janome the bobbin has to go in a certain way. If I put it in wrong then I have to take it out and flip it to unwind the other way.

twhvlr

I get those kind of stitches when I forget to clean the lint from the bobbin area. I try to remember to clean after each bobbin but if I only have an inch or so left to finish a project, I will get lazy, finish, then forget when I come back to sew the next time.