I think what you have there Fefe is exactly as Devs said a female bristlenose. If you look closely at the sides of the face(mouth/cheek area) in the first belly side pic you posted, I can see tiny bristles, really short and barely noticeable. In the male they are much more noticeable. Don't you think your plec looks a whole lot like the lower fish in this pic

?This is a pic of 2 bristlenose plecs. The top fish is the male. the bottom fish is the female. Both are albino bristlenose.
Now, I did some research and it seems that the common pleco is always brown or black. Here is a pic of one

It reaches an adult sze of 18 inches and commons of 1 meter are not uncommon! The bristles are very much smaller.
You may also think you have a rubbernose and the female albino bristles do look a lot like the albino rubbernose. The teller is the teeny bristles.( I have 2 rubbernose plecs.) Occasionally the female will have no bristles but most usually they will just be very short and slight. If there are absolutely no bristles on any of your group of plecs...you can assume they are albino rubbernose.
Basically there is a huge conflict in scientific info about plecs with literally several hundreds of variations of the species I read! There is evidentally a lot of confusion about identifying. Within one group there are also variations labelled with numbers rather than names.
That's just what I think from what I have read. Maybe someone else can help you better.
PS Also your plec is not as spotty as mine. I believe the rubbernose are more spotty. Yours has a bristlenose pattern on the body as in the pic above? Don't you think?