It's certainly possible you are either over reaching as in a build up of harder than usual workouts and getting yourself very fatigued or even over training as in a chronic state of fatigue including hormonal imbalances that can take a while to bounce back from. The former is pretty common and a planned part of many training programs, the latter isn't as common as many folks think especially for riders focusing on sustainable aerobic fitness as opposed to those doing a lot of intense short anaerobic interval work on a regular basis (including frequent high intensity racing).
There are a lot of good warning signs to help you know when to back off a bit and take some extra rest and there are good tools based on power or heart rate or even training hours or miles that can help folks manage workload. For folks that don't use one of these tools (e.g. TRIMPS, WKO+ Performance Manager, etc.) then you can always go with the safe but conservative approach of taking an easier week every third or fourth week of training.
The serious warning signs I look for includes unexpected mood shifts, fatigue that doesn't go away after an easier couple of days, restlessness and insomnia after hard training sessions, high waking or at rest heart rate. There are many others, but the real question is whether unexplained things are happening off the bike after periods of harder training that don't go away after perhaps a complete rest day and an easier and shorter ride or two.
Too many days completely away from training and off the bike can cause problems as well. Most folks feel pretty sluggish after taking three or four days completely away from training and often need several days of easy to moderate riding before they're ready for higher quality workouts. So it's a good idea to limit complete rest days and use some low intensity active rest days when you need a breather rather than completely hanging up the bike. Same for 'rest' weeks, when you do need a rest week consider perhaps an extra day or two completely off the bike but mostly replace your normal longer or harder workouts with shorter more moderate to easy rides to keep your legs moving while avoiding additional deep fatigue when you're trying to freshen up a bit.
Bottom line, everybody needs to come up for air occasionally and balancing workouts with rest is important but based on what you've posted no one can know whether you're over reaching or over training at the moment or whether you're working at a good level. The back to back century rides (especially as these are your first such rides) is definitely a warning sign and I'd probably back off a bit on the midweek training (but still ride) between those weekends but that won't necessarily force you into a chronically overtrained state if you're pacing those long rides, feeding yourself well and getting sufficient rest off the bike including good sleep on a regular basis.
If in doubt, swap a few of your normal training rides for short easy spins and take an extra couple of days off here and there but unless you start showing the sort of warning signs listed above or start losing your interest in cycling I wouldn't worry about it too much. OTOH, don't try to keep up this pattern of long events and weekday training forever, take a weekend off every once in a while and back off your weekly training from time to time if you want to stay in this for the long haul.
Good luck,
-Dave
