What should i do about my job?

I worked as a fork lift driver in a warehouse for 4 years

a member of staff in the tradeshop was sacked for stealing, and my boss offered me his job.

said it was better money ect.. so i took the job.

i started work in the tradeshop and was being trained by the tradeshop manager.

i was there for 2 weeks, and the manager signed off sick with depression.

i was basically told by my boss to carry on with the job, on my own, after only being partially trained for 2 weeks. (the manager blamed stress of the job for the reason of depression)

i have not had ANY break, lunch or any sort of 'sit down' time for over 2 months now, have been told i cant take any holiday or sick until they get someone in to cover me

(i suppose ill have to train them up too? even though i cant do everything myself now)

and the best bit, im also doing the managers work while he is off but have not got any pay rise or even any thanks, support and general recognition for the work im doing?

what should i do?

how can i sort this situation out?

i feel like going off with depression too?

im stressed out too!...

help please.