It usually pays to start all over---remove-replace the needle,re-thread (completely)top thread. remove, rethread, replace the bobbin. right now,top tension is way too tight because it pulls the bobbin clear to the top. and bobbin may be too loose, but start with the top tension. only move 1/2 of a space at a time. willing to bet it is the bobbin.
you did not change threads ? change what thickness you are sewing on ? you may need to change the PRESSURE.