i recommend you restart the level (you only have to redo the helo part) until get to the drop off with at least half health. this is one of the harder levels, it is long.
you can run up to the truck when it is coming and if you watch it a couple of time, you will see where to throw a gernade before they get out. there are two guys behind the left bunker and i think one or two on the right. stay back and use your sniper rifel. the smoke bombs will help becuase you can shield yourself with it, run out in view of them and they will not see you. it will also light up your hud telling you where the enemies are. after that, take it very slow. your rifle will go through some parts of the brick wall. there are alot of enemies. let me know if you need help after that. just take it slow.