Been taking 37.5mg effexor (venlafaxine) for 2 weeks, my doc incresed it to 75mg. is it normal to increase dose after just 2 weeks?

Yes & no: Presumably you're taking venlafaxine (effexor brand is discontinued in states) for major depression, in which case you really don't want to stay depressed, right? In other words, you want to get well & feel brighter as quickly as possible. I checked www.Epocrates.Com which states that you can increase your dose every 4 days (er form every 4-7d)! so work w/your doc. Don't forget counseling, too.

Yes: I probably would have raised it before 1 week in my practice.

Effexor (venlafaxine): Yes, gradual increase from low dose is the norm, as tolerated, until reach therapeutic dose.