I know I have a faster let down on my left side, so Mimi prefers that side. My let down is a little delayed on the right, and before we started solids, if she was really hungry she would get kind of mad when I put her on the right side first. She would pop off every now and again and fuss. She got used to it though and now actually sucks harder on the right side when starting out. (I have always fed both sides. I didn't start BW until she was 10 wo, and I figured it wasn't broke, KWIM?)
I would keep offering the right side. I think your lo will probably get used to it eventually... Mimi did. If it's really a problem, you could try pumping a little bit first, just to kind of get things moving. Hope that helps!