My ua showed erthyrocytes at 0.3mg/l. i was dealing with a yeast infection at that time - could that be the cause?

Unlikely: unless it was a severe yeast infection where the tissue is so raw that there is blood. Most yeast infections are not a source of blood in a UA. If you are on your period or recently had a period, then that could sometimes be a source of blood. I recommend repeating the UA after all your symptoms have cleared to make sure there is no longer blood in the urine.