Are you "clinically depressed"? Surely the Dr diagnosed you as showing symptoms of depression? Most anti-depressants help with sleep ...so you can't be sure but one thing I urge you not to do is change doses without speaking to your Dr, different dosages can have different effects and be targeted at a range of issues, some doses can infact induce insomnia while another aid sleep, some can sedate you down and other doses lift you up.
Please don't play around with anti-depressants, go back to the Dr or have a word with your health visitor about alternatives to taking anti-depressants but please, please don't mess around with your dosage.
You could also ask the Dr if your Health Trust offers managed self help support for your symptoms. Some trusts have psychologists who run short support and strategy training for folk suffering anxiety from post pregnancy to long term depression, so worth asking. This can be delivered via video link re Covid, if your Trust has the service.
But above all be kind to yourself and though not a magic pill relaxation exercises & breathing can help when anxiety plagues your thinking.
You only get withdrawal if you suddenly stop taking them ... coming off is usually stage managed and not always by reducing dosage ... again talk to your Dr. They can't force you to take them but they may offer other ways to support you. Also anti depressant can help with sleep but also inflate anxiety in the first few weeks.
Take care and being a new Mum can be the best and worst of times, so just try to take each day as it comes, tomorrow isn't here yet. X