Once you call your doctor ASAP - and every doctor has a 24 hour answering service - you can ask him to call your pharmacy, so he can renew the prescription on the phone. Since you're on Effexor (Venlafaxine), due to its 4 hour half life, your doctor is more than likely aware of the withdrawl symptoms if you stop taking this medication for a few days, so he should be expedient in his reply. You can then pick up a new prescription at the pharmacy. Also find some way to work with your insurance in raising the quantity of your Effexor (Venlafaxine) beyond a 30 day refill prescription, even if it means getting a new insurance. My insurance allows me to have a 90 day prescription count, so I can avoid the monthly visits to the pharmacy. This also entails putting the payment on credit, where I could pay any residual cost my insurance won't cover, at a later date.
By the way, you and your doctor should discuss raising your dosage of Effexor above 75mg. It is the minimum recommended dose of Effexor, when someone first begins their use of antidepressant medication for the management of depression and anxiety. If you have continued on Effexor past a year, and it seems for you it's been several years, this means your doctor feels you should be on the medication, not as a temporary measure, but as a medical intervention for a damaged brain. Staying at 75mg will more than likely lead to tachyphylaxis. Google that word for more information.
Forgetting to refill your prescription, after loosing some pills, to me, signals a sign of apathy. It could be the start up of a depression that may get worse, if you don't better manage your medication, which I think, should be raised at a higher dosage.