Firstly
If the brake fluid reservoir is above the minimum level then the level of pad shouldn't make much of a difference but don't JUST TOP up with fluid or else it will overflow when you do change the pads- Mind if you've just bled them they should be full so be careful later
The other main possibility is that the brake servo has a vacuum leak so that you are not getting the assistance you would normally
It could also be that one (or more) caliper is sticking so that it doesn't get to grip the disc
If the brake fluid reservoir is above the minimum level then the level of pad shouldn't make much of a difference but don't JUST TOP up with fluid or else it will overflow when you do change the pads- Mind if you've just bled them they should be full so be careful later
The other main possibility is that the brake servo has a vacuum leak so that you are not getting the assistance you would normally
It could also be that one (or more) caliper is sticking so that it doesn't get to grip the disc