I will answer some of your questions quickly, when to gank : after you get a buff, try to get red buff, hit level 2, and then look for any lane pushed up. If no lanes are pushed up, then you need to go back to farming. This is when you can also look to counter JG. Further more, you should always look to gank ANY lane that the enemy is pushed up on. The are practically FREE ganks! if no enemy is pushed up, then you need to go back to farming.
The main reason your behind a level, is because the other JG is just faster. They cleared the jg faster, and tried to gank, and leeched some minion EXP, something like that. That's usually the only reason to be behind, unless the enemy JG actually kills you and then takes your jungle.
If you can't beat the other JG 1 on 1, it's because they counter your pick. Like, Elise, will SHIT on a Lee Sin at level 3, there is just no match there. Her little spiders will do all the work for her. Or it's because they had a buff, and you didn't. Like dragon buffs, red buffs etc, buffs help A LOT.
As to your lane question as to why every lane wants you to gank at the same time, that usually means all the lanes are failing, and that is NOT your fault. A lot of people like to blame the JG for their mistakes to make themselves feel better about losing a 1on1 or a 2on2. However, it is your job to try to help them as best as you can, whenever you can.
You just gotta accept that there will be matches where you as a JG will not be able to help. You WILL get those team mates that blame you for their mistakes, and you need to mute them.
Concerning why nobody goes in with you on a gank, did you ping? Did they have mana? Did they have their ult? How low HP were they? ETC, stuff like that. Sometimes they just don't follow up because they didn't expect the gank. And did not pay attention to their map, that's why you ping multiple times when running to the lane. Other times, it's because they couldn't follow up. Minions could have blocked them, no mana, CD's etc.
Objective wise, you want to look for Dragon fights when your bot lane gets a kill, or even your mid lane. You want to make sure you have more folks there, so the enemy can't contest the fight. After a successful bot or mid gank is the ideal time to go for Dragon. It means the enemy team will not be able to SAFELY contest the fight, and that's when it should be an easy free dragon. Same thing for Baron after 20 minutes, if your team grouped mid and got a good pick, but won't be able to push a turret, it's incredibly easy to bait the remaining 4 enemies into thinking your going to Baron, you slaughter them, then you get a free Baron!
Hopefully this helps, good luck, message me if you have any questions regarding my responses :D