as one who has invisible friends myself... I know that I have complete control over them when I want to... even though they can be pretty spontaneous when I let them have their own way.

I'd be taking two tracks if I were you.

If I felt that I wasn't in control of things (ie: if your problem is more than a creative and active imagination)... I'd be looking for mental illness issues like schizophrenia and I'd also be looking for some Christian deliverance ministry in case it's something demonic.

I'll be praying for you mate.
Blessings
Cat.