Would it be seen ok to change PhD more than once?
Only you can decide how unhappy you are in a given situation, so what action you should take is up to you.

I can tell you how such a CV would come across to me, though.  It wouldn't be positive.  It would look like your decision-making process doesn't have enough thought behind it, and that you're likely to make important decisions and then change your mind. 

The quality of work you've done might get you an interview after someone has drawn such conclusions, it may not.