I stopped playing now I've forgotten it all!

I'm not sure if someone has done this before!
But i'm sure there has to be a way!

I played guild wars for months and years on end! Then i took a break because of my uni.
Now i'm back and I can't remember which expansions i've finished or where I'm up too!

Is there a way to figure out if i've finished an expansion?
Or do I just have to sit there for hours looking over the maps?

You can just look at the final mission of each campaign. Prophecies = Hell's Precipice, Factions = Imperial Sanctum, Nightfall = Abaddon's Gate. EotN = A Time for Heroes. For partial progress you can find mission lists on Wiki and see which was the last one you did. If your characters were carrying mission books you could check those as well.

If you have eye of the north, simply take your character to the Eye of the North outpost and in the Hall of Heroes see if you can add statues for

Eternal Hero of Tyria, Cantha, or Elona, if you have, or can add those statues, you know that you've completed Proph, Fac, and Nightfall in that order.

Aside from that, just check what quests you have in the "Primary Quest" portion of your quest log, those should pop you on the path to completion.

You don't need hours to check the missions, it takes 5 minutes - just look at the icons. If the mission icon is plain, it hasn't been done. If bright, it's done. If it's pierced by spears/swords, it's done with bonus.

Prohecies: do you have mission outposts in the ring of fire islands?
Factions: are echovald and jade sea explored? Is there a mission icon right next to kaineng city?
Nightfall: do you see the blue icon that allows travel to Realm of Torment?

Okayy!
You guys are amazing. I scowered the map for god knows how long But gave up trying to look at all the mission points.
So i followed Gennadios's advice.
Turns out I've got the Tyria and Elona statues.
So i'm guessing I am yet to do Factions?

That would be correct.

You could also start a new character.