could i be premenopausal or going threw early stages menopause at 40

hello all well just alil story about me I'm 40.. just turned 40 in January.with 4 kids oldest 23 youngest 6..over last 2 years I've had off n on health issues from gallstones to being sick. then I started getting healthy working out eating healthier.etc..wells last couple months me n hubby been talking about TTc but not really trying..well I'm currently on my 51 cycle day 23 days late. my periods last couple months have been pretty regular never missed a period or skipped one inless I was pg..well went into doctor today they did another urine test was negative I was dizzy had bad migrane and blurry vision felt faint .been getting bad migrane headache alot lately anyways I was told I could be going threw premenopausal or premature menopause..like WTH really that's the last thing I would think of how do you truly know.I swear I'm not ready..and I don't think im having menopause symtoms..I guess if that's the cause there goes all my hopes and dreams of having another baby.. beyond broken hearted if that's what's going on I'm not ready...