TRAPPED IN JOB

I am stuck in a deep hole and I can’t find my way out, can anyone help?
I joined a private school in a new position as an ‘estate administrator’ and my line manager promised me that it was going to be a busy job and had big plans for me. I struggled to keep busy and ended up helping over colleagues. After 6 months my line manager left to go self-employed (only been at the school 8 months in total). I think he got fed up with the people in his team as are not particularly friendly and don’t like changes.
Since then I have hardly do anything during a day (probably 3 hours a week). I was 2 months without a manager and now the new manager started 2 months ago he is struggling to give me work. I had a conversation with the school bursar and he said that I could assist the transport manager and my job title will change…but knowing the school it will take months before this actually happens. I don’t see it filling up my day and it will be very mundane boring data entry type work. He said he didn’t want it to be seem like he was trying to polish a turd but that is exactly what he is doing!! He said he wouldn’t be surprised in the near future if I did hand in my resignation as found a better job! Is that a hint that he actually does want me to leave as knows my ‘job’ is pointless?
Whilst at work I job hunt online, go on every website I can think of and apply to on average 4/5 jobs a day. I graduated in 2008 and have 8 years of full time administrative roles. I have had some interviews and got a few more lined up. The feedback is always that I come across well but they have gone with someone with more relevant experience. It is getting frustrating to say the least.
Lots of jobs I don’t apply for because they ask for certain amount of experience in a similar role or ask to have used certain systems like Sage and I haven’t. I thought being a graduate would help me but it hasn’t made one bit of difference. I’ve thought about becoming a childminder at home but think it’s too risky as might not be regular income and don’t know my area that well. I thought may be doing an Open University course like an MBA could be an option but decided against that because it will cost £4K and won’t have the time.
I am on antidepressants and if I wasn’t I think I would have done something irrational by now – like walk out on the job. However, I have my 3 year daughter and my financial commitments to consider – mortgage, childcare, car costs etc. This is the only reason why I am at work! So basically they are paying me (quite well) to job hunt!
Another thing I have to consider is my daughter is starting school next year and would need to cut my hours (as only one that drives, husband is on a provisional licence but can’t be bothered to pass test!) If I hang on at the school I might be able to negotiate less hours (considering I do nothing).
I can only envisage me being at the school getting more unhappy, wasting my skills, brain power and may be going onto another job eventually which has a pay cut with mundane work. May be I’m too ambitious for my own good but always thought I would be in an important well paid job (though didn’t know what). People always ask what you do for a living and judge you by what you do and hate having to say I’m an administrator (though don’t actually do anything, except going stir crazy as so bored and I’m sure I’m losing a brain cell everyday as not using it!!)
The only thing I can consider is proposing something to the school but not sure if it would go down well and may be someone else can give me some insight?
I could suggest that if they would evaluate the support roles and see if there is any short fall and if some assistant is needed in something. I could job share, or have a couple of job roles at the school and for them to consider me doing school hours from next September?
Otherwise, I have not a clue where to go from here except going round and round in this endless self-pitying depressing cycle that is consuming all my thoughts and effects my mood and self-worth.