I suspect there is no solution to this problem, but it cannot hurt to ask. I recently met a wonderful woman and, while we have only been together a few weeks, we can envision being together the rest of our lives. The one fly in the ointment is that she is very tight and I am pretty big, and we have not been able to have sex that is pleasurable to her. We have tried it a couple of times, but it just hurt her and if that continues to be the case, I don't want to go there again. We are mature and experienced and know about lubricants, etc., but this is just not working. We enjoy toys and oral too, but damn! We want to have sex.
"I suspect there is no solution to this problem"? Way to get me interested in answering your question there, dude.
There are size-discordant couples who are just never, ever going to fit, but they are necessarily kind of freaky and unless both halves reside on the extreme opposing sides of your basic human-variation bell curve, it's really not that likely to occur.
You'll need to figure out what exactly is happening here (we know what's not happening) before you can craft a solution. Is she really too tight, or too short front-to-back, or capacious enough but not managing to seize control of her own semi-voluntary muscles? If she's too tight or too clamped down, or if you are actually that great rarity among men, the Guy Who Is Too Big (no matter how many used to call the San Francisco Sex Information line claiming membership, that is one exclusive club), she may be able to accommodate you with a little work. Using fingers her own or yours or geeking out and acquiring a set of dilators or graduated dildos may produce results (the process can be variously entertaining, tedious, or traumatic, depending). If she is too short, well, there's a finite amount of space to work with but adjustment of angle can move things around in there to a surprising degree (make sure you're sliding under her cervix, not into it). And be sure her legs are as far apart as comfortably manageable it's amazing how much the internal topography can be altered with some external manipulation.
And finally, I need to point out that you are already having sex! I totally get that you want to have intercourse, and I would like you to have some too, but all that stuff you're doing already? Sex. Do some fingers, some oral, some shallow intromission and some X-treme frottage (a lot of lube, a lot of careful positioning, and a lot of wet sliding). Have orgasms. Follow with cuddling. Do you really not feel (and look, and smell) like people who just had sex?
I've tried three different vibrators and, without exception, they left my labia and clitoral hood numb and swollen for a day afterward. In fact, if I rub my clit with my fingers (my preferred method for orgasm) too vigorously or too imprecisely just a few millimeters off or if my fingers aren't wet enough, the same thing happens. And partners can't suck on or even lick my clitoral hood for too long, to say nothing of rubbing me with their fingers. Is this a serious medical issue or just another prank of human physiology? Also, I hated coming with the vibrators: it felt like my body was just going ahead without me, and left me irritable and unsatisfied. Am I the only woman in the world who doesn't like vibrators? Have I just not found the right one yet? (Experimentation in that regard has proven depressingly expensive.)
You're just a sensitive girl and, yes, the victim of a physiological prank. (Nicely put!) I suggest using barriers between yourself and any stimulation-producing member, human or otherwise.