When does your uterus start to get hard?

Hi ladies! I need a little advice. I have a doctors appointment on Tuesday (just my regular physician and then an OBGYN appointment in January) but I'm curious to know others' experiences. For the last week-ish I have had bloating in my abdomen/pelvic region. I'm not skinny by any means, but this is different than just gaining weight. It definitely feels like there is something in my lower belly, and it feels a bit heavy. My stomach is protruding a bit (much more than usual) and around my uterus feels hard. My breasts also feel/look bigger and firmer, at least to me. I have taken several pregnancy tests (just cheap ones) over the last few weeks but all are negative. I was diagnosed with PCOS a little over two years ago. I've been taking Metformin and prenatal vitamins for several months now. My last menstrual cycle was late August/early September. Going that long isn't uncommon for me, but if I go that long inbetween my period is usually at least 3 weeks long. This time it was just a week! Which was awesome, and I attributed it to the Metformin. I've also been taking Levothyroxine for Hypothyroidism for 2-3 months. My question is, has anyone had experience with their uterus/lower abdomen becoming hard, getting negative tests, and yet being pregnant? My husband and I have been trying for a long time now and I really hope this is it. Should I buy "better" pregnancy tests? Could my hormones just be too out of whack to test positive on a hpt? I've attached photos of my belly. The first is kind of how I typically look (I'm sucking it in) and the second is how bloated I've become. I'm sorry for the long post, I just don't know who else to ask until I see my doctor.