Well, although it's best to have some sort of documentation of harassment-related issues to backup your claim, it's not always completely necessary if other facts can be proven. One of the main reasons most people don't complain (in-person or in writing) to the employer or file a complaint with the EEOC is because they're afraid of being fired. This is taken into consideration by the EEOC and the Court. Also, the fact that you are a single parent and cannot afford to be jobless would also be a good reason for not having previously complained in writing. If you do not receive child support (deadbeat dad issue), then this would also help to ground your reasoning.
You do, however, have (or can obtain) documentation evidencing that you've received good job reviews for the past 10 years, and after your breast reduction, you received a bad review, and along with your allegations of harassment, this would probably suffice as enough evidence to present an issue to the EEOC and possibly a triable issue to a jury. As to your claims, your credibility would, of course, be challenged by the employer, so if you have a clean criminal record and have otherwise proven to be a good citizen (no prior "strip joint" jobs, etc.), then this would certainly help with any sexual harassment claim.
There is something I'd like to ask ... whether your breast reduction was paid for by you, personally, or your medical insurance provider. If paid for by your insurer, then I would assume you were having back-related, or other problems, and that is why the surgery was covered under your policy. If that's the case, then the employer can dispute your reasoning for having the reduction, and I would not use the reason for having the reduction solely to make yourself less desirable, as this could damage your credibility to some extent. Your breast reduction does still, however, help to substantiate your claim as to the timing of the harassment and demotion.
Witnesses can also help to support your claims. If you file an EEOC charge and name witnesses, the investigator is supposed to interview those witnesses and obtain statements during his/her investigation. The EEOC investigator has 120 days to complete the investigation. If you do not receive the Report of Investigation within 120 days, then you can write a letter to the EEOC and request a "Right to Sue". In any event, after the "Notice Right to Sue" is issued, please be sure to request in writing an administrative hearing within the time specified on the Notice. This will keep you out of a formal court proceeding, and an EEOC administrative judge will hear your case.
I'm not trying to advise you as to what you should do, but if it were me, I'd file an EEOC charge immediately. You can fill-out the form yourself, and the EEOC will usually assist you in completing it. Once you file the charge, the EEOC will assign an investigator to investigate the matter. Oh, of extreme importance: Be sure to state that this is a "continuing harassment" in your EEOC complaint, as this tolls the deadline for your not having filed the claim previously. If you are questioned, then just explain that you were afraid of being fired.
Something else you should be aware of ... once the EEOC complaint is filed, if your employer continues to harass you or even fires you, then that's considered retaliation, and it appears to me, from what you've posted, that your employer is probably well aware of its potential liability as a result. In any event, if that does occur, then you would need to amend your EEOC complaint to add retaliation and/or discharge. If you do amend your charge, then the EEOC investigator's timeframe to complete his/her investigation will extend from the date you amend the Charge. Just make sure you read all documents you receive from the EEOC and calendar all deadlines. And, if you need further help, please just let us know.