I'm pretty sure that you cannot do ROTC for pharmacy school. At least I could not, but I also was not prior enlisted.
There are some considerations to make here. Time spent in HPSP is NOT creditable for retirement, even though you are in reserve status as a 2LT.
I would do Guard/Reserve, because that time would be creditable toward retirement, then apply to become an officer after you finish pharmacy school (Them agreeing to allow you to become an officer and change MOS is not a given however.) Then do HPLRP. This all hinges on you going to a cheaper pharmacy school near a Guard/Res unit of your choosing, and whether said unit has an opening in your MOS. You would however be on the hook for 5 years instead of the standard 3. (3 accession + 2 HPRLP). Note that this only works if you have <56K in loans. (HPLRP pays 28k/yr after taxes.)
Otherwise, I would get out and do HPSP or GI Bill.
It should go without saying that you should not be on active duty enlisted and go to pharmacy school at the same time.