How about using a global match?

$ perl -e '
my @toCheck = qw{ A B };
my $string  = q{2A 3B 4B};  
foreach ( @toCheck )
{
    my $count = () = $string =~ m{$_}g;
    print qq{[$_]: $count };
}
print qq{\n};'
[A]: 1 [B]: 2 
$
[download]

I hope this is useful.