OP, I'm another one who had to move back with my parents. Well, it's my dad and he doesn't have a basement since he lives in a detached row house in a complex. I have my own room and bathroom though for which I'm grateful. Still, I'm 52 and thought I'd be much better off than I am now. But, the bottom line is, it's tough for many people now and there's no shame in working at whatever job you can get. Yes, help out your mom and tell the truth as you have zero to be ashamed of. Don't let yourself feel sorry for yourself though after an initial getting used to it period.
As others have said, make a plan and be proactive while also considering what is good in your situation:
1. You have free rent and a minimum wage job. This means you will have some money each month that you can control how you use and also get the things you need: gas/bus fare for work, clothing, meds, etc. It's also commendable that you don't consider yourself too good for a minimum wage job. OP, you aren't a loser, but a hardworking guy!
2. You have time to spend with your mom who was nice enough to give you the basement to live in no charge. So, do what R39 does and you should feel honorable to help your mom in anyway she could use. Discuss it with her and if she insists there's nothing, then you find ways whether it's yard work, cooking, cleaning or whatever. Spend time with her too as most mothers will appreciate that, but also have time to pursue your passions.
3. You have no rent to pay each month meaning more time to pursue things. Education or could you start any kind of business? If not, don't feel bad. What are your passions? Whether it's art, writing a novel or something else, you have time to try to make something perhaps marketable since you're not paying rent. Whatever you do, make sure it's something you're really passionate about that will also help you feel better about yourself.
4. Clean that basement as someone else suggested to scrub out the smell. Also, get rid of all that childhood stuff -- except for a few things -- a page out of a coloring book or stuff to keep in a scrapbook maybe.
You've got a chance to start again even if it is back at home in the basement. Fix up the basement really nice as you can. White or light yellow paint to brighten things up? Paint old furniture? Add a hot plate on a sturdy table to go along with the fridge? You have your own space and can help and spend time with your mom too.
Good luck OP and again, good for you for taking that minimum wage job. Keep up your hardworking spirit and things are bound to get better.