TTC when seriously irregular

My husband and I are actively TTC but my cycle is ridiculously irregular. It was approx. every 3 weeks for a few months when he was deployed but now that he's back I'm on CD 57 with 3 false preg tests.. Sometimes my cycle is 3 weeks, often somewhere between 60 and 90 days but sometimes it's up to 120 days apart... my doctor claims I'm just naturally irregular and there's nothing to worry about... but idk, I think it's pretty sporadic and should've received a second look or testing to ensure it's okay. We want to conceive so badly and I worry about how hard this may be given I don't know when I ovulate. I've tried ovulation tests before with no luck... I don't know what to do. I've been taking prenatals for awhile now and my mom told me she started taking a Vitamin B complex in high school to help regulate her periods. I've started taking Vit B in hopes it'll help but believe it's too soon to tell. Any advice?