if the jobs are pretty self explanatory by the title you dont need any explanation really,
and if you do, just write a basic list of job tasks - like data input, reception duties, stock control etc
dont write it in 'prose' like - i was responsible for doing this when that happened and making sure so and so was ... etc
how old are you? you can get rid of a lot of stuff from when you were a teenager or stuff regarding school exams.
if you do different jobs, consider creating 2-3 CVs separating the stuff.
you can always overlap wth some things and make reference to the other stuff in and opening statement
i work freelance in 3 depts and i have about 10 CVs... and i make reference to my skills in the other linked depts - it shows versatility and transferrable skills.
it is also fine to go over 3 page if necessary - if its 3 pages of waffle then no, but if each role is relevant and important, then include it ... no company is going to say "well, they are perfect candidate, just what we need - but their CV was 6 lines too long, so they are out" ... are they?
also consider reformatting it - i have no formatting on my CV, it gets too awkward to adjust as things change - it is basically - one line with year, company name, production title, production type, and my role - then if necessary a line or two of explanation - then a blank line, then the next one
get rid of columns and double spacing etc, if thats why its so long.
also get rid of any personal hobbies etc - not needed.