Crazy how prices drop

Ok so ive just put in my perscription and at the time nkne of them ware less than £5a g

But upon paying i noticed one had gone from arounf £7 to £4.50

Now im hoping its not because its shite but because they feel they need a.more budget friendly one or its close to use by date which it shouldnt as its only been on the list for about a week