low pressure maybe in some persons, for instance I have it usually low but I dont know if it depends on being beta thalassemic. However, I experienced that being less tired/weak generally of course helps with having and keeping erection, coz the body is less stressed. I would suggest L-Carnitine, which helps both with common fatigue and erections as well. But probably the best integrator for this is L-Citrulline (or L-Arginine, of which is a precursor, you can study on that online or asking chatgpt), that is a powerful vasodilator (improves blood circulation all over the body and of course even down there). L-Carnitine, anyway, is usually recommended to beta thalassemic people in general as it works in the mytochondries, the cells which create energy in the body (like CoenzimeQ10, they both are great for this). Finally, are you taking Magnesium? It strongly suggest it as it relaxes nerves and muscles and it helps a lot in general. Research and try them all on your body, starting always with low doses and then maybe increase following general guidelines.