Need guidance. For better understanding?

Hi Doctor, All my reports are looking normal so far, and my husband's sperm analysis is also normal and within range. We have been trying to conceive for 4 years, and 2 year of marrige i tried I previously took Clomid for 3 cycles but dio not have success. Last October, I completed 2 IUl cycles with Letrozole, but they were unsuccessful as well. I also had ultrasound scans done, and no one told me that I have PCOS or PCOD. This process has been very stressful and emotionally difficult for me, and I am feeling depressed about the situation. I would like your guidance on what would be the best next step for us. Should we try one more round of IUl, or would it be better to move directly to IVF? I never use met form can i use met from and try iui Every 21 or 22 of my period my progestrone levels are 11.2 only What is lagging i dont understand please suggest me what can i do Is there any test i need to do for better understanding?