At my undergraduate school I was hired by my advisor to work in his lab. Now I want to apply to graduate school at the same institution and have begun asking for letters of recommendation, but the only responses I've received have been no, I'm unable to write letters at this time or I'm at a meeting (conference) and will reply when I get back (not automated and I'm pretty sure the prof is already back because we work in the same building).
The other people still haven't responded and it makes me think they're either really busy and can't do it and so are delaying informing me they can't do it or they didn't see it or saw it and forgot about it. The deadline is approaching quickly.
Is it obnoxious if I email them again to ask if they received it or when I can expect a response?