When I am investigating a topic, I find a couple of articles that I liked and review their references. This helps in locating reputable journals, books, and other studies. It also helps you narrow down your search. I then read those articles and review their references. This helps save time, effort, and frustration. When I was in college I was given access to the ERIC database of journals. You might want to try that website (http://www.eric.ed.gov/).
The following is a list of journals that I was able to find sickle cell anemia referenced in:
The Journal of Clinical Investigation
New England Journal of Medicine
Journal of the American Medical Association
British Journal of Hematology
Journal of Pediatric Hematology/Oncology
Take any title of a major medical research publication, such as the Journal of the American Medical Association, and go to their website, such as the one linked below. Then in their search bar type in what you are looking for, "Sickle Cell Anemia" and the most recent or most popular journal articles will come up in an organized list for you.
The New England Journal of Medicine is another one that has a great reputation, and I've linked that below too. In this way, you know that the journal articles have a very good chance of being accurate, referenced and well written, and will have credibility with the research and academic community.
It is difficult to obtain many articles from medical journals for free. Other journals to try in addition to those listed by the other posters include Blood, Pediatric Blood & Cancer, and American Journal of Hematology.
Alternatively, you can access the Guide to the Management of Sickle Cell Disease from the NHLBI for free. The URL is http://www.nhlbi.nih.gov/health/prof/blood/sickle/sc_mngt.pdf - it is a bit outdated but will likely meet your needs.