Looking at another clinic could not hurt, and might help. Take your embryo reports from your ivf's with you. This will help the RE see what is going on..I have seen several ladies switch clinic's and then become successful. I say go for it!!!
It wouldnt hurt to have a consult with a different clinic to see if they would approach your case differently, its surprising how protocols can vary with the different clinics, also if you havent done so already look into having acupuncture done before and after transfer, it increases success rates in ivf by up to 60%