Does ptosis normally get unacceptably worse throughout the day even after having surgery 6 months ago?

Best to see your surgeon or an oculoplastic surgeon for evaluation. Eyelid ptosis can get worse as the day progresses and your effort to keep the eye open weakens. You may or may not benefit from additional ptosis surgery. Need proper consultation to determine. See following link too.

You most likely have the heaviness of the eyelid all the time.  The issues is the what is the brow doing to compensate for the upper eyelid residual ptosis.  Internal ptosis (Mullerectomy) is highly popular.  Unfortunately it is not good for many eyelid situations.  In particular it is not effective when there is an underlying levator disinsertion.  The fixing is fussy but it is possible in many eyelids to strengthen the anterior levator using an anterior incision.  There is no substitute for a personal consultation.  This surgery will also fix the crease height issue.