Hi,
If you think you are eating fewer calories than you need to maintain, but you're not losing weight, one of six things is likely happening. These are in decreasing order of likelihood, roughly.
1) you're underestimating calories. I know you said you measured stuff, but it's easy even if measuring to underestimate, especially on the hard-to-measure foods. Try weighing.
2) you're overestimating your maintenance caloric needs. Online calorie estimators are just estimates, and have no way of knowing, for example, how intensely you work out during those 3-5 hours or whatever you typed into the activity section of the calorie estimator.
3) you're compensating for your diet elsewhere by not getting as much exercise OR non-exercise activity (and thereby not burning as many calories as you think). This can happen without people even knowing it -- e.g., they may fidget less throughout the day, and fidgeting burns calories. Maybe not a lot, but some.
4) your body is holding on to water, and a "whoosh" is right around the corner. (Note: if you've only been counting calories for a month or less, I'd elevate this to #1 or #2 on the list.)
5) your hormone levels are off, and you need thyroid meds
6) you are the first known exception to the laws of thermodynamics, and should be hustled off to a major medical institution for study and dissection ASAP.
Good luck,
Kim