Sorry you are going through a rough time. Please try stay calm, I was exactly the same as you every ache and pain was worst case senario in my head.
I had siatica after my Trach as I was use to being so active it was,n honestly, worse then the pain I felt after my operation I almost threw up in pain. Have someone masage the balls on your lower back and your leg it will help.
For months after my operation I had stomach pains and back pains i asked my nurse and she basically said that when you have a trach you tamper with nerves that lead to your bladder and bowel. This means that going to the toilet can sometimes be more paintful and it feels like a sharp pulling pain when moving etc. Anyway as your body is in pain it mans your position when you sit/lie is compromised giving you lower back pain! It makes so much sense when a nurse expains it to you like that. I also think that casue you haven't been to the loo in a very long time this may be making it worse. Get some laxatives down you and hopefully it'll make you feel better.
In regards to the weeing, when I came home I found it hard for about 2 weeks I would go and it would either dribble out or nothing at all. It is basically your bladder coming out of shock it will get better over time. It might be worth checking with the nurse though as I was not allowed out the hosiptal until I had wee'd a certain amount.
I hope this eases some worries!