I had a Singer with same problem. Had it to repair many times and finally hauled it to the landfill. Don't have time to deal with these problems.

Is your presser foot up when you thread?It sounds like your thread is not in the tension discs.It's easy to make that mistake and will give you the results you are having.

As a last resort take your machine into the repair place---when mine did that and I took it in and there was a piece of thread caught in the upper tension---no way could I have fixed it myself or even thought that it was the upper tension
They reminded me to cut the upper thread and not to pull it out from the spool of thread---hope this helps

Have you tried holding the bobbin thread between your fingers when you begin sewing, I have to do that with my machine.

Coats & Clark thread isn't made well any more. It used to be wonderful thread, I've been sewing for over 40 years and have seen the changes in thread over the years. I use Gutterman,Mettler and Aurifil threads, they are so much better and give far less tension issues. I sew with modern Pfaffs and antique treadle machines too. The cheap plastic machines just aren't up to snuff; get a better machine, the older machines from the 50-60s are made better and are much less fussy.(getting off the soap box now) :)
Sharon in Texas

Tension problem
 

my husband who is a former industrial sewing machine mechanic says to check the top tension and to make sure there is no lint in the tension disc for the top thread. Hope that helps

My husband who is a former industrial sewing machine mechanic said to check your top tension and the tension disc . Double check the way it threaded too. Hope this helps . He's my go to guy 😄

All my suggestions have been used, but I think the bobbin could be in the case wrong.

When I had this problem recently (loopy thread on the underside) I checked all I could think of. Then I decided to take off the needle plate (the removable plate under the presser foot) and found some lint and a little piece of thread under there. After cleaning it out, all was well then.

I'm not familiar with your model of Singer, but I have a Singer H74 that has the spool post on the horizontal--I find when I use the optional vertical spool post I get better tension. Also when my bottom thread on the Singer or my nice Elna, it's usually because the top thread has come out of the take up arm or the tensioner discs--maybe from "jumping" a thick seam intersection,etc.