Need advice about self certifying and resigning!

[InfraRed2015]

Hi all and thanks for taking the time to read my post.

I started work with a new company 2 months ago. I am currently studying for my Masters which is a part time course but still very demanding, and I needed a not too stressful part time role to earn some pennies alongside. I originally applied and was interviewed for a sales assistant role, but then the area manager phoned me and said I had been assessed for a senior sales role because of my experience so invited me in for that interview too. I got the job, and my contract was 20 hours a week. Perfect I thought! Not so perfect anymore. What I didn't realise was that once I am fully trained to become senior sales (I am still sales assistant at the moment as I needed to do my training) I will be running the shop alone with just one other person at VERY stressful and busy times. My mistake really but I have realised this week that I cannot continue. I currently work my ASS off in that shop (I really buzz off serving customers, I love being busy), there's queues out of the door at times and on almost a daily basis I am being told that I am not quick enough, and to hurry up and "chop chop". I couldn't go any faster and I am in a position now where the thought of me managing the shop for a 12 hour shift in the absence of manager just fills me with dread. I have Uni deadlines to mee and my manager is already piling the hours onto my rota. I need to put a stop to this now, not only for my mental health (I have suffered with depression, anxiety and stress before and this is coming back) but for the sake of the company who are about to invest in my senior training. The place cuts corners because they are so understaffed, they took hours from me one day without telling me meaning I turned up for work lol and I just can't bear to be told that I am not doing my jobs quick enough anymore!! It's a sad situation because I felt so positive about my job when I first started. It's not an option speaking to them about not being senior (pride and embarrassment-I would rather just cut all ties). My plan is to phone in sick and then self certify for a week-speak to my GP and send my resignation letter ASAP. Please can somebody advise what to say when I phone in sick and also what to write in my letter? References aren't a problem-I won't be using this employer as a reference however I won't be leaving a bad taste in my letter, I want to leave as amicably as possible. I am a creative person, I make and sell jewellery, am part of exhibitions and I really think this job is killing my creativity and passion.

Thanks once again :)

[holeinmyheart]

Gosh you poor thing as you are suffering. However I so want you to be truthful. If an amazing intelligent person like you, finds the job impossible for a human to actually do, what chance has anyone else got ?
I want you to resign but tell them honestly and succinctly the reason.
You write so beautifully here.
Your employer cuts corners because of the staffing situation, NOT YOU.
You don't need them for a reference so why not tell them the truth. Maybe they will learn something? You can write to them in sadness, not in an accusatory way.
Best of luck. Hugs

[InfraRed2015]

Thank you for your lovely reply holeinmyheart !!

I am in the process of leaving, I will keep you updated :)

[holeinmyheart]

Ok. I am glad you are leaving as they don't deserve you.