I have two kids that are 18 months apart and I know what you mean... it is exhausting! (They are almost 2 years & 4 months old.) I'm a SAHM, DH works long hours sometimes, and we're not near family that can help... so it is mainly on me for the majority of their care. (We did just start daycare two mornings a week for my youngest, so that my older daughter can do a mommy & me swimming class and soccer class the other morning... so I'm down to one child for a few hours twice a week.)
We originally were going to try the daycare more than two mornings a week, and it was this crazy schedule of one girl was there one morning, the other girl was there the next morning, and one morning a week they were both there for four hours. I only lasted a month, and found it wasn't for me. The daycare was supposed to be a "break" for me (since DH has had to work more hours in this new job), but I found that getting them out the door and to daycare by 8am on the mornings we didn't "need" to be anywhere (i.e. mornings ODD didn't have classes

) was more stressful than just keeping them both with me all day! So I think that month long experiment helped to refresh me, but also helped ease my perspective somewhat... we do still have the two mornings so that I can go to Mommy/tot classes with ODD... so maybe a few mornings or hours of outside help a week could help ease things for you?
And I also go to bed super early... my whole family giggles at me, but they know not to call after 9:30pm - because I'll be in bed!!

The kids are bathed and in bed by 7:15pm/7:30pm, giving me a few hours of adult only time - but otherwise the sleep is more valuable to me at this point than doing anything else at 10/11pm...
So I can definitely relate!! There are moments some days where I want to pull my hair out and the times when they both need something or are crying are the worst... but like you, I just keep hoping (and looking for reassurance) - some day it will get easier!