Can an antidepressant become less effective after a few years?

Increased my dose of Effexor 3 times in one year (I've been taking it for 25 years, following my childbirth and my difficult pregnancy) Hello, during the last year, I experienced personal difficulties in June, my MD increased my Effexor dose to 37.5. In December, another misfortune, my sister gets sick and a lot of worry, my MD raises my dose to 37.5. At the beginning of June, again start to feel anxiety symptoms, so now I'm waiting for Effexor to take effect in about 3-4 weeks, but I'm at the maximum dose (225 mg). I suffer from generalized anxiety normally well controlled with this medication.