To OP - YANBU, but don't panic, 17-month-old boys do get less whiny etc with time, and they do learn how to challenge all that physical energy as they get a little older! I was in a similar position to you a few years ago; my DS was a nightmare (or so I thought at the time) ... but now I realise that he was just a very high-energy, lively boy who literally needed to be exercised like a dog every day! He wouldn't sit down and watch TV quietly, but was constantly on the go, breaking things, pulling off the skirting boards, trashing the kitchen while I was cooking etc etc ...
But he doesn't have ADHD or anything like that, and he is now a perfectly "normal" 5-year-old. Fresh air and exercise were the key for us, and whilst it was tough being pregnant with number 2 (who was born when DS was 2 & 3 months old), he loved her from day 1 and was a fantastic older brother right from the start.
So - yes, boys this age can be very very hard work - but it doesn't last for ever, and it is perfectly normal to dread spending time alone with them! I echo everything that everyone else has said re. going to lots of activities - have you tried the physical ones like TumbleTots etc which usually have loads of little boys with like-minded mums who are dying to meet other mums with boys!
Also, you're not mad to be thinking of having another baby, but it might be worth a chat with your GP first if you have suffered from PND before - he/she may be able to suggest some coping strategies for you...
Good luck, try not to worry, you are very very normal and it does get easier, I promise.