Tefillin Dilemma

I write lefty but do most of everything else right handed (ambidextrous). I have, since my bar mitzvah, davened with my arm tefillin on my left hand. Recently a rav told me I must start putting it on my right hand for it to count.

I really don’t want to do this, as it would feel awkward and I’ve been putting it on my left hand my whole life, however if it makes it halachically valid then of course there is no discussion.

Another Rav said to me he too is a lefty (in writing) and still puts tefillin on his left arm because he CAN, albeit not as well, write with his right hand, and the same is true for me – I can legibly write righty though not as well. I think this is the reason I was given normal tefillin at my bar mitzvah despite technically being left handed but I can’t recall.

What is the truth? Do I have to switch?