Your paystubs are viewable on the UPSers.com website, not the Teamsters app. As for as your schedule, you should talk to your business agent. Different regions can have different rules, but only getting 3 hours notice if you're working is likely not OK. UPS can lay people off, and it is done by seniority so being new means you get cut, you need to check if you're actually laid off or if they're just telling you not to show up. If you are being laid off, look into filing for unemployment. If you aren't, show up and demand your 3.5 hour per shift guarantee that you are entitled to as a union member.
Information pertaining to your business agent may be found on your hub's bid board or your local union's website. A shop steward may also be able to assist you.