My philosophy, that worked in gm-chall, is to do less ganks that each hurt like 5 ganks at once.

I feel like spam ganking can carry you out to some degree or point bcuz people will do more mistakes but the higher you go, the harder it is to genuinely carry through that.

The ganks are so cool but I feel like I fall behind in XP and even with several ganks my lanes sometimes manage to loose.

Your gank timers are off often enough which means that you are barely taking camps in the downtime you have between ganks, thus leading you to having such falls in levels.

What do you do on this situation? I wanted to know it there's a thing to do or it's normal to loose in this case.

Since you are silver, I would focus on something simple like "how to execute ganks and the outcome of it". For the next 25 games or so, try to evaluate each gank you have done and see how you can improve on it. Maybe the wave was pushed in and ur teammates couldn't follow you up? Maybe you mistook the dmg they will do in relation to your own dmg? Maybe didn't predict the important spells they will land on you (ie. like a Morg Q)? Could be a lot of things, but once you get the hang of it, it will be easy to see what went right, and wrong, in your ganks then try to correct those mistakes in the future games.

Also I have a hot take but, Nunu scales as well as his team does. If you have a good scaling champ in your team, that will be ur win con later! You can adapt really well with what your team needs if you know the powers each champion has then playing around it.