If I had my time again I'd still do medicine. I am a realist, so I won't deny that aspects of it suck, namely:
1) The government - pushing their destructive agenda and trying to destroy the service on the sly
2) The system - it's big, it's old, it sends you to **** places without caring about your personal wishes/family/social life.
3) The hoop jumping and exercises in pointlessness - starts when you apply and apparently never ends.
4) The media - they help the government achieve their nefarious aims.
And these are just the ones I can come up with off the top of my head when I should actually be revising. There are probably a hundred more.
HOWEVER - I defy you to find me a single public sector worker (teacher, nurse, police officer, firefighter etc) who is currently happy with how the government is (mis)managing their place of work, who isn't underpaid and over worked, and buried under a mountain of shitty paperwork and targets and being **** on by our disgustingly obsequious media. This is the price you pay for caring about your fellow man/woman in England it seems.
So I certainly empathise with any doctor or medical student who hates that we are being screwed and wants to get out, but the grass isn't necessarily all that much greener on the other side for a lot of people.
That said, medicine does come with all sorts of added stresses which other jobs don't have to deal with (very long, exhausting, expensive training, emotional demands, being sent all over the country, etc) so I would agree with whoever told you that if you can see yourself being happier in another job, to do that job. This is why work experience is so important - so applicants can make a better informed decision about whether this is actually the kind of life they want to have full time or not.
Speaking for myself, the good bits outweigh the bad so I have no intention to pursue other avenues.