Rarely Bottom and Need Advice

Not sure if this is the appropriate sub for this, but here it goes. Anyone have advice on relaxing enough to get it in and minimizing pain? I rarely bottom, and always have a hard time relaxing enough to get the guy inside me when I do. And when I do, it tends to hurt and burn a lot, and I just can't seem to get used to it. I now a part of this is because of how I'm built (I'm 5'2), so if any shorter, stockier guys have anything to say, please let me know. Thanks.