When to stop TTC

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I'm not even sure which board to post this on because I fall into so many different categories... I've been trying to conceive for four years, had three unsuccessful IUIs, one fresh IVF cycle (MC at 6 weeks) and one frozen IVF cycle (MC at 10 weeks). I know some people have been through much more, and those ladies give me strength, but I don't know how much longer I can stay on this journey. My doctor has a few more tests to run, but says she and the other eight doctors at her practice are stumped. Am I amiss to think about stopping... or should I keep pressing on? I feel lost.