How many g net carbs are you eating per day? At a certain point your body MUST go into ketosis, there is no guess work about it. But if you're eating more than, say, 40 or 50 g net carbs a day, then it starts to get iffy.
People have different responses to being in ketosis. Some people find their breath and pee smells different. Some taste copper. Some taste sweet. I just get really, really, really thirsty.
Oh also, ketone testing strips are notoriously unreliable, unfortunately. If your goal is to go into ketosis, drop your net carb intake down to 20g and you'll be there in a few days.