I have got a 3rd Class when I did my undergraduate studies in Economics, I have 3 years of work experience in Pwc as an auditor, but I am not happy in this field. I would want to study further. But then I don't want to pursue a career which everybody is pursuing, I see myself studying Environmental studies, developmental studies. Since I didn't score well, I am stranded, there is no decent university that would want to take me (I am not aiming for IVY league) but yes a decent reputed university. My only choice is to do another degree. But then I am 25. I am not an american, but I would like to study in USA or Canada.

Sure, you can do as many degrees as you want, BUT you will need to fund them yourself..