In general we distinguish between needing a pantyliner and a pad. If a pantyliner is worn because of staining or discharge, either to avoid stained underwear, or to avoid the discomfort of wearing damp underwear, any stains found on the pantyliner may be disregarded and you would not be considered niddah.
However, if the pantyliner is not sufficient to contain the bleeding and a pad is required (or if a pantyliner is soaked through and needs to be changed several times a day), you can assume that you are experiencing a flow and would be considered niddah.
If showering once or twice a day enables you to avoid wearing a pantyliner altogether, it does not seem as if you experiencing a flow. It is difficult for us to make an actual ruling since only you know how frequently/heavily you are staining, how often you are showering, how much staining you are experiencing compared to your actual periods, etc.
Please feel free to get back to us with any further questions.