Firstly, regarding Tax Credits, they are calculated based on income for the previous tax year, but if your income is significantly different (which it is due to maternity leave) then you can ask them to calculate based on your current circumstances and estimated income for this tax year.
Secondly, if you're renting at the moment, you're likely to be eligible for housing benefit - have you applied for it? If not you should apply ASAP, through your local council. Usually you have to apply online on their website. You should apply for Council Tax Reduction (sometimes called Council Tax Support) at the same time.
Thirdly, you will probably be eligible to apply for social housing (council or housing association) and you should contact or visit your local council to apply. Bear in mind that if you're already "adequately housed" you won't be very high priority.
I don't recommend moving in with your parents because you wouldn't have any legal right to stay there if it didn't work out, and the council could argue that you'd made yourself intentionally homeless by giving up your own tenancy.
I suggest you visit/contact your local Citizens Advice - take your Tax Credit letters, payslips and rent information with you - and they will be able to calculate your benefit entitlement, check the tax credit decision was correct and help you challenge it if it wasn't, and advise on your housing options.