I am in a similar position to you and have posted a lot about it on here. DH works long hours, travels a lot with work and so I'm on my own a lot. Loneliness is a big part of the problem.
Things that seem to help me:
- some nursery for them both (youngest only started recently and I can really feel the difference - just knowing that you have a few hours' breather in an otherwise long week)
- exercise
- a hobby or goal to work towards for YOU
- a cleaner just to remove some of the drudgery (OK I know a lot of the daily grind can't be avoided eg washing, cooking, endless clearing up but at least if scrubbing the bath and vacuuming can be removed it's something)
- befriend other SAHMs - a lot of the mums I know work part-time and it's their salvation, but unfortunately I can't - logistically, financially - so at least with other SAHMs you get real moral support
I keep telling myself "the days are long but the years are short", it's my mantra and in dark moments I have to cling to that.
I've taken ADs and although it took the edge off, there were other unwanted side effects. I did CBT for a while and it was this that helped me the most - it made me feel a bit proactive about helping myself when I felt utterly trapped and powerless and counting the years till they're both in full-time education. I still have days when I do that, don't get me wrong!
I found a really nice HV who said things like "don't feel guilty for looking forward to 7pm" and that was helpful. It IS hard, there is no denying it, and most working mums I know admit that their days at home are tougher than their days in the office.
Re finances, it has taken me a while to realise that although we cannot "afford extra help", that sometimes, extravagant though it seems, getting a bit of childcare is more important than other things in the budget. It may well have saved my sanity and my marriage.
Another thing, if your DH/DP can give you a breather at the weekends - few hours child-free time - it will be good for you, for him to have alone-time with the children and also nice for the DCs who are with mum all the time. I find everyone benefits (but especially me!) from a change like this.
Sorry for the essay! You are not alone.