|Check the position of your bow hand to make sure that the grip is firm enough that you will not lose the bow, but not tight enough to be a death-grip.
Early in my playing career I reached a point where I squeezed that thumb into place so tightly that I developed cramps in the right hand. That severely hampered my playing. I could not play delicate notes. I did not have the flexibility necessary for more advanced bowing techniques.
I don't know anyone who believes that the right hand position is perfectly natural at first. I have never met a first year violinist who wasn't uncomfortable holding the bow. But after developing the proper grip it you will find that it becomes perfectly natural and comfortable.