work restrictions under hsmp

hi all
would be grateful to any who could resolve a few issues for me:
i have been working in the uk for 1 year as a doctor, and have recently moved to a hsmp visa valid for 2 years. in view of the current job situation for overseas doctors in the uk(quite difficult to get a job in a chosen speciality), i am wondering if:
1) even though my skilled field under hsmp is as a doctor, can i work in any other profession or field, for example, as an employee in a company unlelated to medicine. or is there a strict rule about adherence to working in the field for which hsmp was given?
2) can i hold 2 jobs concurrently?
3)will working in a different field for a few initial months have an adverse impact on my hsmp extension after 2 yrs ? ( i understand one has to show evidence of being economically active in the 2 yrs, and having worked in the field for which hsmp was granted.)
thanks !