Lump above left breast, had ultrasound but it was gone by then after being there a month, now its back, what can i do?

Get it again: If it comes and goes like that it could be a cyst. Get the ultrasound and possibly fine needle aspiration while it is still there before it goes away. Also, sometimes these lumps appear and disappear coinciding with your menstrual cycle.

Ask for a biopsy: Clearly you are very worried about this lump. Breast lumps come and go, and as a surgeon i've seen many "lumps" that were really just normal tissue that got firmer and then softer with a woman's period. But i always offer a needle biopsy as an option for "peace pf mind, " and many women took me up on it. One of them is a very good friend who thanks me every time i see her. It's ok to ask for it.