yeah, it’s pretty classic to feel like you must be losing your marbles cos something is definately wrong, and to grasp at straws and feel exasperated over and over when whatever you think is your answer this week, turns out next week to not be it, then to feel that it must be in your head, and start the cycle all over again. i’ve been there. repeatedly. 
have you thought about going to see someone like a well qualified, upto date, general practice psychiatrist or a psychologist whose background isn’t entirely focused on, but definately contains solid adult ADHD knowledge (eh, maybe even both- i’d do the psychologist first, cos they’re not so med-centric- i bet you can check on their specialisms online, or ask their secretary what they focus on- as an open ended question) and *not* telling them what you think you may have. instead you could just say that you feel that you’re struggling, and have been for as long as you can remember, and that you’d like to see what they think- and ask them to give you a thorough checkup/onceover/general asessment (wait to see what they cover during their assessment- they’d do a history to start with, which’d likely bring up issues, past diagnosises, etc, then i’d expect them to test your IQ, working memory, verbal skills, etc)?
then if they come up with a result of ADHD, it’s not due to your prompting or steering them that way- it’d be down to what the test results and history point towards (you can’t really cheat those sorta tests without a lot of practice!)…. and if they don’t, *then* you can suggest it as something thats been stuck in the back of your head for a while as a possible, and ask them to consider it as an option, and rule it out/tell you why it doesn’t fit- again, putting the onus on your results.
be honest with them about your concerns (that you feel you might be a hypochondriac, and why, that you’ve been on meds- and what, and why, and how they affected you). if they start off working with cognitive behavioural therapy, any benefits you see from that will be really constructive whether you have adhd or not… (win:win!) if you get started with meds, you should expect to feel a change within a month or so (sooner from stimulants- non stimulants can be a bit more subtle and take more than a few days, but changes don’t take months to appear)- so it’d not need to be a huge drawn-out year long process any way that i can imagine…. and coming on and off ADHD meds after a few weeks isn’t like coming off say… long term effexor use (for me, that was way less than fun).
perhaps just don’t tell the friends and family what you’re doing and thinking is wrong, this time around. do they really *need* to know? why? or do you just feel the urge to share? in a way, you’d just be putting undue pressure on yourself and putting yourself in the spotlight by involving them at an early stage- it’s kinda like telling everyone about your upcoming driving test or possible pregnancy- if you give everyone the date, then they’re all psyched up, fussing and watching you, waiting for the news, and you have to deal with telling them the bad news if you fail/turn out to not be expecting, and the accompanying comedown- instead of going through that fuss, you can always tell them that you took the test after you’ve already passed/it’s for sure happening, and share just the celebrations.
if you need to share *something* for some reason beyond your blurty mouth and desperate lack of impulse control (welcome to my world! ) you could always just tell them that you’re going to be making some lifestyle changes, and to be aware, and let you know when/if they notice any difference in your behaviour over the next few weeks. or you could ask them to reflect on any possible perceived changes retrospectively, after you’ve started on a treatment strategy- if you can manage to keep your mouth closed for that long (i’d fail epically, but trying is worth it!). 
personally, i’ve always been oddly private about stuff that really matters, when it comes to sharing with my family and friends (though in classic ADHD style i’ll blabber way too much information in graphic detail at people who don’t matter to me- strangers on the bus, etc – i know, i know! ) . with family, i want to spare them the upheaval, and myself the natural influx of wellmeaning advice and opinions from people whom i respect and trust, and accordingly might not entirely appreciate total frankness from- cos it’d hurt more if it turned out that what they had to say wasn’t exactly what i wanted to hear…..