I mean it's really hard to answer these questions.
1.If mid and bot are both feeding to the point that they are 3 levels above you, there really isn't anything you can do. You could gank their lanes and help get a few kills.
2.If you are the ADC (Attack Damage Carry) you should be getting the cs bot. Generally top is a solo lane (most likely at your level it's a duo because there is no jungle) so it's quite hard to get cs when there are 2 people in lane
3. Nocturne isn't supposed to be a top in the first place (he is played as a jungler) so that already puts you at a disadvantage and top champions are MOSTLY bruisers that are not meant to carry but to take damage (eg Shen, Nasus, Malphite, etc...). This being said it is much harder to carry when playing top lane, instead the APC (Ability Power Carry) which is mid lane and the ADC which is bot lane should be carrying. Hope this helps.