Current waveform distortion on transformer with a load resistor on secondary winding
The white waveform is the magnetizing current for the transformer. With an ideal unloaded transformer (a pure inductance), this would be a sine wave that is shifted by 90&deg; to the right (lagging) from the primary voltage. However, your actual transformer is operating close to saturation, so you start to see those odd narrow peaks at the top and bottom as the effective inductance drops.

The yellow waveform can be understood as the superposition (sum) of the white waveform plus a second sine wave that is in-phase (0&deg; shift) with the line voltage. This second wave represents the additional current being drawn by the (resistive) load.