The business sounds like piss takers. They just don't want to pay for a full time person on reception.
If it is not a large company then it really might not seem cost effective to have a full time receptionist, especially if it has been experiencing financial difficulties. My experience in medium size companies has been that when times were good they would have someone on the front desk at all times, but when there were cut backs this would get covered in some way by existing staff. In smaller companies then they have hardly ever had reception staff, again this is managed by existing staff.
OP, I think that, as others suggest, the most constructive way to tackle this is to push for some FAQs. There are surely only a limited range of questions? Perhaps have a list of names as to who knows the most about particular areas so if you are handling a query you really can't answer you can call the expert directly.
You said:
bully for you for picking up litter. Honestly I would have taken the job if I had known about reception. I e worked in the sector for many years and have a lot of experience and knowledge in my area. I feel it's a waste of my time sitting at reception.
In a previous job I had there was a rather unpleasant issue with a toilet (I will spare everyone the details!) Suffice it to say the cleaning contractors were refusing to deal with it. In the end one of the senior managers, a woman with many years experience in her field, just slapped on some rubber gloves and sorted the situation herself. I feel that is a lot more unpleasant and a bigger step down than a few hours covering reception, but she gained a lot of respect from the staff for doing that.