Co worker telling lies to get me fired...

Today at work a co-worker went to one of our managers and told him that I am not doing my job and that I said that I didn’t want to be there + plus more but I forgot (oops) anyway, all of what was said was completely untrue for starters I don’t actually speak to anyone (which I guess I should but I’m not a talkative person) so me telling anyone that I don’t want to be here is completely absurd. (I think it tho, doesn’t everyone?) so I guess they can read minds?? Idk. As for not doing my job I couldn’t help but laugh at that. The only reason I can think of why that was said was because I was walking around the department looking at shelves to see what needed stocked and everything was looking good except for kiwis, and I went to the back but we didn’t have any so I had nothing else to do, so I made busy work looking for rotten food and that is when I was told to see the manager. I’m really upset and honestly disappointed with this job. I do everything excepted of me and then some. I constantly see groups of co workers standing around talking and doing nothing. I see them on their phones, calling and texting, literally full on phone calls while they are on the floor, but me actually doing my job gets me in trouble. Honestly makes me want to cry. I’m back at work again tomorrow and the next four days straight yay. I’ve only been there three weeks and I can just see this getting worse. I’m really want to look for another job because if this is how I’m going to be treated I’d be without a job. Any advice for me??