No, the jungler typically won't help you unless you have a kit that can lock them in place and then follow up, otherwise its a waste of their time.
EDIT: If you can hold them off 1v2, then your team should be able to get alot of advantage elsewhere. ESP if you tell the jungler that you will be fine most the time.
When I mean farm, it means to get the gold from far away, but stay out of the enemy's dmg zone. If you are using Jayce, poking those minions are a good idea, but you want to make sure you aren't pushing your lane. There are lots of videos on youtube on how to freeze a lane, make sure you go check them out. Then you go into a custom game, set up 5 bots and you try 1v2ing them as practice. You want to try to keep the minions between your turret and the brush (assuming side lanes), but the turret is not hitting them. Even if they are being hit by the turret, make sure you know how to CS under turret. Again there are lots of videos on how to CS under turret. Go check those out too.
If the enemy is harassing you alot, it means the following:
- you are pushing your lane too far
- They have some awsome long range poke (e.g Velkoz / Lux / Nidalee / MF / Cait)
- you aren't dodging those skill shots properly
in scenario 2 & 3, you can improve my playing better. But in the scenario that they know how to freeze and harass, you'll need to buy those potionss inorder get CS. Either that or forfeit the farm but still stay in range to get exp.
EDIT 2: You may need to get blue potions as well if you need mana to spam to get CS.
EDIT 3:
The most important thing is actually to not die. That comes before CSing. You know you will be behind already in CS, so don't also be behind in terms of exp and levels. You loose both exp, CS AND map pressure when you are dead (or rather, they don't need to pressure you anymore, so they can roam and cause a ruckus elsewhere.)