What Causes Weakness, Shortness Of Breath And Tiredness?

My husband has weakness, shortness of breath, trouble sleeping, light-headedness and is very tired. He had a few episodes on our holiday and got a tentative diagnosis of vertigo. Since then his doctor discovered an infection after getting a stool test done. He s taken 17 of the 21 tablets prescribed, but a side effect of metrinozole is shortness of breath so his doctor stopped it. A ride to emergency in an ambulance, sitting in a waiting room then going to see his doctor came up with stematil tablets( again). All his obs have been normal and no one seems to know what it is. He s very fit, doesn t like taking medicine or being ill. Any ideas? It sbeen over a monthnow.