Welcome Pink, another one saying speak to the GP and school. I agree with Runner, the earlier you seek help the better, once issues become embedded and things teach crisis it is much harder.
Zoo thinking about and deciding what to focus on is a huge step. Have you heard anything from sixth form yet?
Freedom if recovery is complex the team should have, or be able to refer to, someone DS can speak to.
Runner OT is usually more practical based with the aim of giving DC the tools to cope and solve problems themselves. For example independent living skills, improving their ability to cope with everyday life, understanding and recognising emotions, helping DC cope with sensory differences.
Kind Young minds have a parents helpline. If your DC is waiting to be assessed or has recently been diagnosed with something like ASD Scope have a parents mentoring service. There's also various courses such as Earlybirds/earlybirds plus/cygnets for parents of recently diagnosed autistic DC. You can also ask your GP to refer you to your local IAPT service if needed, depending on your area you may be able to refer yourself.
Once you are being seen by CAMHS there are various courses they can refer you to - from sensory courses to filial therapy to NVR training, although parent led CBT isn't big in CAMHS. Books depend on how old your DC is.