Hair colour fade is annoying and it could be because your hair is now white underneath the shade you apply. However, if you live in an area that is hot and sunny this will not be doing your delicate strawberry blonde no good. I suggest using a shampoo and conditioner that is designed for colour treated hair. Plus a colour protection spray that has an anti UVA/B filter, that you can apply before styling and before you go outside.
Maybe altering your shade to a slightly deeper one can keep it from fading so quickly.