At the moment I’m on innersense I create hold gel...it is expensive though, so possibly not a great buy to experiment with gel.
I wash, put my gel on while it’s soaking wet, then i plop for a bit - tbh scrunching it with cotton does the same thing, but putting it in a plop means I can go do something else and I’m lazy, lol, and diffuse it till it’s about half dry, stick a bit more gel on and finish diffusing it and scrunch the cast from the gel out. Then clip it up at night and cover it and I can get 4 decent days out of it till the curl goes, nope. I could not wash it longer in that it’s not dirty at that point, but there’s no point trying to refresh my hair, it’s as much hassle as washing and doesn’t give great results.
I have really fine hair though, so it gets build up very easily and things like oil are a huge no.
What you need will very much depend on your hair and curl type - but if you’re getting noticeable build up after just a few days... your hair doesn’t like something you’re putting on it 
www.facebook.com/groups/curlygirlrejects/?ref=share
This Facebook group might be handy if you’re just starting to work out your hair... there’s also loads for the curly girl method - but that can be a bit full on and daunting when you’re at the, well I’ve stopped straightening, what do I do now? Stage.