How soon can I use Alpecin shampoo post FUE op?

If you have concerns about scarring after surgery such as keloids, it is best to discuss this with your surgeon.  Anyone can give you a general answer but the actual outcome is your doctor's responsibility.

Every doctor has their own specific post operative instructions. Please give your doctor a call.  Otherwise follow general washing instructions or same methods you have been using.

It looks like you may be experiencing shock loss from the hair transplant surgery. Generally the majority of this hair comes back. I would recommend you follow up with your doctor who can examine you in person and better discuss what exactly is going on.

Photos of your hair that has fallen out cannot give a diagnosis. It is normal to lose hairs after surgery.  If you believe it is not normal it is best to contact your doctor for a follow up exam.

There are no special creams to use after surgery. Some doctors may recommend anti-bacterial ointments.  Ask your doctor for specific recommendations.

It is probably too late to think about if wearing a hat could have affected your surgery. It probably wouldn't but if you're concerned it is a good idea to follow up with your doctor.  If you cannot see your doctor in person, you can email your doctor.