I remember the feeling well, and I had a DH to share the load, so I really sympathise. Doing it alone must be hell.
You need some time to yourself. There are a few babysitting websites you could investigate to find someone near you. Find someone to do a regular slot evenings and/or weekends. Look at HomeStart in your area. They train and provide volunteers for a few hours a week for families with pre-school aged DC who need support. I volunteered for them for 6 years when my DC were high school age, precisely because I remembered how tough those early years were.
Join a gym with a creche. I did this. Sometimes I'd actually use the gym but often I'd veer off to the coffee lounge, pick up a newspaper, have a coffee and switch off for 2 hours. It was bliss.
My youngest drove me to distraction and although I loved her I really didn't like her for a long period of time. Exercise helped - burning off energy, getting her into sports at an early age, anything to wear her out (run to that tree, now run to that tree, I'll time you, see if you can do it faster this time, yay you're so fast!).
I now have DGC and recognise the struggles my daughter is going through, so I do what I can to help take some pressure off. I hope you have some family who can help.
Keep reminding yourself this will pass. You'll look back one day and wonder how you got through it, but you will get through it. Before you know it the years have flown and you'll be on MN giving advice and support to a mum just as desperate as you are today.
You're only human, you're doing a great job in tough circumstances. Be kind to yourself.