I've seen this a lot, and I want to write a long post:
You need to vent off in some way.
it's not like repressing your (natural) passions is going to do you well anyways, doing that accumulates frustration subconsciously too. This doesn't necessarily mean that you are forced to sex or masturbation, but even having physical contact with other people (girls if you are straight), will help you ease the pressure of nofap.
Your brain has been conditioned to:
>accumulate enough sexual energy
>get horny
>give a reaction to the body about this
>the conscious mind accepts/doesn't argue back this command
>you masturbate
So if you keep denying the conduct that you've normalized over years, the mind needs to resort back to one of it's primal ways: wet dreams. You feel bad because it's like you've failed yourself, but it was completely unconscious. What you are trying to do is change the conscious mind so that the unconscious can learn the new habit (which takes 90 days according to what people say, but personally I think it depends on each person). It's normal and just how things go.
As I said, you need to put your sexual energy to use or just keep doing what you've done, but keeping in mind that wet dreams are a certainty (they aren't bad on themselves). You can actually try to use your saved energy to try to talk to girls or make a new female friend that can help you vent off. Many physical interactions can make your brain get horny, but also ease off the pressure of not doing anything. Gyms are also a possibility, but it changes your whole lifestyle. Sports has been the universal way to put our sexual energy to use, with the added benefit of having fun in the process, even playing table tennis might help tire yourself out.
What you need to keep in mind is that even if you consciously think that abstaining from physical and sexual action is good, your most primal part of the brain doesn't understand this, and with a good reason, in the end you are an animal that wants to keep the species going, so if you kill your sexual appetite like a monk or a saint just because of nofap, you aren't doing yourself a favor either. Having sexual thoughts about girls is fine, but as long as you have the willpower to determine when, how and with what you want to masturbate. It's about conquering yourself and all that, which sexual asceticism does too, but I assume you want to have a gf at some point too.
I say this because the mindset of:
>>went through entire day without sexy thoughts
isn't going to help you in the long run, you need to have sexy thoughts, but have the strength to not fall back into masturbating. You might think you are smart and strong because of it, but you aren't, you are weak. It's like trying to block the sun with a finger, the problem is much bigger than just having sexy thoughts and it goes through the depths of your mind. Keep your head up, have those sexy thoughts, but when masturbation is a possibility, reflect on it and inspect the idea. Rationalizing the "horny" thought is far better than just hiding it, because you "kill" it when you think about it well enough, but hiding it just keeps it lurking in the shadows waiting.
Hope it helps.
