If the fundamental concern that has drawn you in this direction is a desire to have children, if you haven't checked out the Billings method of natural family planning yet, do look it up. Might not help, but it would be fun to experiment.
And welcome!
Also, if when you do broach the subject more strongly Lisa gets worried that this evil bunch of polygamists has tried to persuade you to take another wife, do point her back to this thread and the fact that both @Daniel DeLuca and myself have actually encouraged you to find the answer to this particular issue within monogamy, with her. Our focus isn't polygamy, but marriage, and that first and foremost means her marriage to you. It might also hypothetically include discussing another marriage with us at some point in the future, but that's only a possibility, while your marriage to her is a certainty.
I completely agree! We've done just about everything short of going to a fertility specialist. The main issue, we believe, is she has a severe hormone imbalance and will menstruate non-stop. The year we got married she did so for 2 years and months straight. It'll get better for a time, and then get bad again. We've discussed possibly finding a surrogate if it's possible, however i kinda think that's a little unfair to the surrogate to carry said child, develop those maternal feelings and whatnot, only to take the child once it's born. And unfortunately we can't afford adoption. Originally, she's the one who broached the topic of polygamy, but we weren't in a good place with our relationship. So, we concentrated on us. Now, our relationship and marriage is the best it's ever been, and i SHOULD feel fulfilled and content, but i don't. I feel like i should be able to offer the same love and support that i do with Lisa to another. Saying that, again, makes me feel guilty. Like I'm failing as a husband because i want to love another in addition to Lisa. I also believe that she rejects the prospect of polygamy now that we are doing so well as a couple. Its all a big complicated mess.