Sounds like your ankles might be falling in. Have a look at yourself walking in the mirror. Do your ankles fall in towards the center??? If so, good orthopaedic insoles could help, I got some for 40euro.
I'm in a very similar situation to you. I'm only 24 but I've been suffering with back pain for 11years. I finished uni last year and begun further education straight away so I am also broke! I put off physio for years dew to the cost and bad experiences. When I would go I found it painful and it made me worse. Some would tell me I had a weak core and give me stretches and exercises to do, it always hurt and made it worse, others would tell me to lose weight (I'm a size 14 but I eat healthy and I used to do yoga and Pilates which made it worse, and I can't exercise for now dew to pain now and damage in my spine), Physio should NEVER EVER hurt, if it does, just change physio!!!
Just like you, When the sciatica would get bad I would just take pain killers and live in hope! 
DON'T DO THAT!!!
Find a good physio. Expect to spend a good bit on getting better, but DEFO don't put if off, it will get worse and you will end up spending a lot more time and money on getting better in the long run. I've already spend over 1K on getting better in the last 6weeks and will have to get a loan off family and friends to continue, I know it will be worth it in the end, But i am on a list for surgery and I find it hard to see an end to it, and I worry about how my education will suffer as I am unable to attend, finance is also a huge worry.
Unfortunatly, I'm in the 'too little too late' category, and orthopaedic insoles could have saved me so much money and pain. I finally found a good physio. She diagnosed me with hyper mobility (basically I'm double jointed). My ankles turn in when I wear shoes with no support, this in turn caused my hips to fall down on my spine causing a lot of damage. My mri showed up 3bulging discs, one of which has a large prolapse. I have lost sensation down my leg and I'm having mild issues with the water works. I am used to being in pain, but the pain I have experienced in the last two months has been the worsted I've ever experienced. Despite the strength of the painkillers and valium the pain is still there all the time.
All I can say to you is get yourself sorted before you get to this stage, it will be worth it!!!!
I'm using insoles called 'bio advanced'. My physio gave them to me. They were only 40 Euro. They help a lot. These might help you a lot. Like you, (back when i was able to walk) I found walking up hill really painful and normal work shoes a pain in the ass! Don't do any activity that makes it worse!!!
I really Hope you find something that helps you get better!!! back pain sucks!!! It's especially difficult when finances hold you back!!! If you can't afford physio once a week, maybe go once a month. Chat with them about your finances. Ask them to give you a discount
Also, if it turns out you have a prolapse disc, just rest. Stay in bed or lie on the floor for 3weeks until the sciatica is gone and use LOADS of hot water bottles.. oh and don't sit or drive!!!!
PS, most doctors are sh*te when it comes to back pain, they will tell you to keep going, but listen to your body, if your sore rest!!! 