I have to buy another bottle soon for the summer months. I take 2000 IU's in summer and 5000 IU's in winter. It depends on where you live also. I live on the east coast on Long Island, in the winter months it is very difficult for us to get enough sun to help us with our levels. I also do not do any dairy, which does have added D.
As a rule, the RX type of Vit D is not the best type to use. It's usually D2 and we should all use D3. Did your doctor take another level after the 2 months? It's very rare for a Vit D level to raise enough in 2 months time.