Successful IUIs but Failed IVF


I will be doing my first IVF in the spring. I’ve had 2 successful IUI’s but now that we are trying for baby #3, the IUI’s are not working (9 months of Clomid/Follistim/IUI and all BFN). I’m just really hoping IVF will work. Wondering if anyone has been in a similar situation. Did IUI’s previously work for you and now nothing works (IUI and IVF)? What caused your IVF to not be successful (if you know)? Just wanting to know in case there is anything I can do or not do that would up my chances.