Colleague and boss picking on me

I feel like screaming, honestly! Work is just so, so bad right now.
I work as a care assistant, and I really do like my job but you do get under pressure because of staffing, and sometimes I am unable to get some things done due to having to do my paperwork before coming off shift. However, ever since I gave them a letter to cut my hours down as I am going to university in September - I have had nothing but horrible issues with them. A colleague who places us in certain places, she makes sure I am on the same floor as her so she can keep an eye and my God, she was TERRIBLE. She had ago at me for walking out of a room after answering a buzzer - reason was because I was going to turn next doors off, then go straight back to her so I can sort her out as the other lady was buzzing for quite some time and we can get into trouble for not answering them quick enough.

Then she had ago at me for having my phone out because I told her a colleague was trying to get hold of her. I had my phone while I was in the toilet to go for a wee, so how is that any issue? It's not out in the open where visitors can see it unless they want to watch me go toilet! She will report this to the management, because they pulled me up before for petty little things that no other senior colleagues has complained about. I am turning into a complete nervous wreck, feeling so down and very upset and not looking forward to going into work and I don't want to feel like that because I love being there when this certain person is not on... It just makes me feel depressed :frown:

I try my very best, but we are not perfect and do make mistakes but clearly she thinks she's the best. Reporting her is a big no no, since she is best friends with the manager anyway.