Oh dear, you’re getting a bit of a bashing here.
It’s really hard with an active toddler. Here’s what I would do:
Slow down. Stop trying to do whatever it is you’re trying to do other than be at home with the toddler. They require much more attention at this stage than they do as babies. You have to watch them like a hawk. It’s wrong to think that once you’re through the newborn/baby phase things should just get easier. Accept this, adjust accordingly, you will feel happier.
Stop TTC. You’re struggling with a 20mo baby. If you are already pregnant, your toddler will be 2.5yo when the baby is born. If you’re struggling at this stage, it’ll be way worse with a baby to look after too. How old are you? Why the rush?
Tell your DH to pull his fucking weight at home. I honestly can’t think of a single job that requires him to have all weekend, every weekend off.
Don’t be a martyr.
You’re not failing and you haven’t failed. Your toddler sounds normal. Everything you’re describing is 100% normal. Relax. Take a deep breath. Give in.
Finally, I get very very annoyed when people suggest going to work as a panacea. All that means is you avoid the difficult bits for some of the week. It may not be best for the child, for the marriage/relationship, the mother’s mental health, workloads, finances, long-term prospects. “Get a job” is possibly the shittest advice ever. However, some hours in nursery each week could be the best solution possible.