Not sure what is going on with my teeth

Brush your teeth not your gums.

So for a while I neglected my teeth, it was because I was depressed and couldn't really be bothered to do much apart from sit in bed. In february I went to the dentist, he had to give me a filling in one tooth and said my gums were bad as they were bleeding. He told me to use a medium toothbrush as apparently soft ones are for old people or something? Anyway, since then I have been really caring for my teeth, brushing 3 times a day, flossing x1 and mouthwash x1. But my gums still appear to be in bad shape. I don't think I brush very hard,but I still have a red gum line in some parts (which I thought meant gingivitis?). And randomly, bits are bleeding, even though I have brushed them and made sure to keep them clean. I started to use corsodyl because I was worried that my gums were still in bad shape. But then I physically watched myself in the mirror lightly brush my gum ( and it bled, could it be the fact that my toothbrush is too hard? I did a little research and most people suggested a soft toothbrush. I just find it odd and pretty concerning that nearly 3 months later my gums still don't seem to be great, at the front they appear pretty pink, but they just seem to bleed randomly and I have no clue what is going on! Does anyone have any ideas? Because I only seem to brushing lightly and then my gums bleed