TL;DR: This year I changed job to a quite toxic company and because I have to work for two different clients in parallel I'm burning out. I need suggestions about telling about my mental health to my employer or request to change clients because of their incompatibility

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At the begin of this year I changed work from a small startup (which was nice, but they didn't pay very much) to a consulting company and since then I'm experiencing my first burnout.

Just to give some context, the first month or two months in this new position were nice: the project I've been put on was difficult, but the other people in the team were very kind and helped me navigate through the codebase. After there quiet months, I've been put on a second project (in parallel with the first one), same domain but different client and the two clients must not know that I work for other clients. This doesn't work particularly well because both of the clients require me a full--time presence and both the teams have the tendency to call you without any warning and without setting up a meeting on calendar and beacuse of this I pass 3/4 of my day on such useless meetings (which many of them I have to be present at the same time, and sometimes one meeting is in English and one in Italian) without getting any job done and now both my leads are getting frustrated by my delays.

To make it all worse, when I was contacted from the headhunter it was for a mobile developer position, but because of my previous position my employer thought that I could temporary work on one java project because there was scarcity of developers and I could be a nice fit.

I'm not sure if I sum up my situation clearly of it's confused (I'm sorry about that), but tomorrow I plan to call my employer to tell him that I can't take it anymore and something has to change, I just don't know if I should put it on the incompatibility of the two clients, my mental health or both