Personally I would go to the same clinic if its convenient for you, I have got a second opinion at the same place without any problems. Go in and tell them the story say you have been previously and would like further testing done before seeing a specialist.

There are many, many reasons for anaemia and a number of blood tests are the usual way to start investigating. Low iron intake can be the problem, low b12 can contribute, if you have a recent history of heavy menstural bleeding. A faecal stool sample is often the first test to check for gastro intestinal bleeding. There are so many different reasons for a low haemaglobin and your GP can order a number of tests to try and narrow down the cause.

Hope you feel better soon