I don't have a child with autism but complex needs so although I don't really understand what you are going through I do know that you need to get support to make life easier at least.
Do talk to your school teacher, or School Governors.
And also get a carer's assessment from your local Social services as you are entitled to this, even if they then tell you they can't provide it all - at least you may have an idea of what you should or could be getting.
If school aren't supportive enough then approach your local Parent Partnership (have a look on the internet), they can tell you what support school could give, and also they do a bit of handholding if you need to attend any meetings or go to appeal.
Also contact any local or national support groups for autism - like Autism West Midlands or National Autistic Society. They can give you support, information, and advice including a helpline, training in behaviour management, or courses in understanding autism. They might also have some useful information leaflets for school with suggestions on how best to deal with a child with autism.
Your local Family Information Service (try searching online or at your library) might have details of specialist playschemes that will take disabled children.
Also look out for the national KIDS charity who provide play & leisure for disabled children. They might be running a scheme locally or if not see if they can set something up locally or perhaps train any local staff in their ways of working with any disabled child.
It might be that initially you need to look at some solutions to behaviour management taking a holistic approach to see what it is that sets off certain types of behaviour. From there you might be able to get some training and support from various agencies mentioned above and it might be a case of one step at a time, but at least it's a step forward, even if slower than you might want.
Keep up the good work, you are a caring person, you want to do the best for your children, but remember ask questions, and don't be afraid to tell your GP or any health professionals you are in touch with if you are finding it difficult. They are there to help you and if you don't tell them you are struggling they won't know. And be persistent. If they don't come back to you after a week or two, ask again - but ask.
Good luck.