Hello and thankyou for approaching DoctorSpring with your query.
I have gone through your case and understand your concern.

Your B.P rise could be related to many factors, like your mood , stress, or autonomic (central nervous system) over activity. The medication fluoxetine itself too could cause a rise in your blood pressure, but right now it is too early to say.
I would advise you to continue with your medications and recheck your B.P in a weeks time.
If it still is high you can consider switching your medication.
Fluoxetine can cause hypertension in about 1%-10% of the patients and Doxepin in less than 3% of the patients.
Do inform your doctor about the change in dose you are taking from 20 mg to 40 mg.
I would advise to change your doses in consult with your doctor. As of now continue the present dose and depending on the following B.P readings you can consider going back on your old medication or other medication options.

I hope this has helped. Feel free to follow up.
Thankyou