How to ask your jungler for help
Yes your lane might be pushed and you might be pressured, but your jungler needs to hear it from you that you are in a position to make use of a gank. While it's his responsibility to have map awareness, he has to show presence everywhere and prevent his jungle from being stolen. And that's assuming he's not counterjungling as well. Every second that your jungle is traveling, he is losing gold and xp. Don't ask them to do something that is going to force them to burn everything to cross the map in time to help you. Especially if you are straight up losing lane. Frankly if you are getting stomped constantly in a 1v1 it's your fault, not the junglers. If you keep losing trades, stop trading.
Secondly if you are asking for a gank don't wait until you have 100 health to do it. Ideally ask while you are backing or if your opponent is very low and if your jungle is nearby. If you need a camp, specify a timeframe. Give them a chance to do what they need to do to set up for a camp. If you need help immediately then you probably waited to long to ask.
Finally if you are 0 and 3 don't expect a gank, at that point the enemy can generally 1v2 and your jungler is better off trying to snowball other lanes.
For the record junglers should be asking their team if they want a gank as well, but both parties are responsible for communication.