Hello
First of all, it depends on the type of orchid it is- Im going to assume its a Phal.
I personally have never had much luck purchasing orchids from local stores whether they be lowe's, tj or walmart-
I bought the most beautiful in bloom orchid from trader joe's- fabulous 3 weeks later the plant doesnt appear to be as happy- most of the roots are dead and a serious infestation going on underneath- my luck huh?..
Anyhow blooms falling off may be due to stress, humidity issues, and possibly root issues (Check!)
Im by no means an expert, but Im sure some of the other members would help you better.
gluck!