If you are noticing at work that the amount of expectations or tasks given are not physically possible to complete in a given time frame by any human being you might just be in trouble. If you express that you are concerned this is the case and ask for advice and get none, or very ambiguous advice then bank on it. This is a common tactic used by superiors.
If your set of “responsibilities” has suddenly changed and your noticing others with your same job title or similar title are not being held to the same unrealistic standard this is a sign of “targeting” by your superior. It is a plan to set a narrative for “poor performance”. If you are performing at your best and it continues to not be “good enough” you should really examine your working relationship with your superior. The next step is to begin to document EVERY SINGLE THING, EVERY SINGLE DAY. Keep your journal of what is expected. Follow up frequently with your superior about what you are getting done and the time frame in which you are doing it. Ask how your performance was on this day or this week it is time to get proactive.
This is the time when details matter. If you have your facts in order about your own performance it makes it much more difficult for a superior who might just want to get rid of you to execute this plan of setting you up. You should always view your job as an ongoing court case with evidence. You should be armed with data and facts about your performance. This is when specifics matter. Your peers might also have insight if they suspect you are not being treated fairly. It is good to ask them to be specific and make record of their thoughts if you suspect your being targeted. Is your superior leaving you out of meetings? Is your superior talking down to you in a hateful or hurtful tone? Document it, times, dates, witnesses. This is critical to maintaining your records.
Finally take deep breaths and relax. You are not superhuman you just have a boss who does not like you and might like to get rid of you for whatever personal reason. The more you arm yourself with your defense the better. Stay alert, observe patterns and continue to do your best. Most importantly keep quiet about your journals and collection of data unless you are forced to defend yourself in a specific situation. Sometimes if a boss “has it out for you” there will be nothing you can do to stop it in the long run. But many are just as stressed as you are and looking for an easy scapegoat to save their own ass. If your well prepared you can make them look ridiculous in front of their superior.