Employer is treating me unfairly

I'm just curious if anyone else has had any issues regarding employment during pregnancy and not exactly being treated right. Fortunately (but also unfortunately), my employer hasn't necessarily done anything to which I can take action against. I work for a small business where I was initially hired as a receptionist, but have also assumed the role of assistant and am now doing pay roll, marketing, etc. and was refused a raise. My list of daily duties has increased exponentially, but my wage has not increased at all. Basically, when I got pregnant, everything changed. I was suddenly being told I was not performing to standard as my job description had completely changed from when I was hired and I was unable to get everything done in a day as there was so much to do, not to mention I had terrible morning sickness and was vomiting every day, and only called in sick on 2 or 3 occasions. The girls I work with are absolutely dreadful to be around as they gossip constantly, and my boss is essentially trying to push me out the door to have her friend take over my job as she knows I won't be returning to the company because of school. Today I needed to take the day off work as I didn't sleep at all last night and needed to see my doctor as she suspected it was something related to my gall bladder. My boss was pissed off to say the least, and told me that I should consider taking medical leave in the new year once business slows down if my pregnancy is "so difficult". 

Basically, I am feeling really stressed out and walked over, and I want to quit, but I don't know anyone who would hire someone who is 20 weeks pregnant. Plus, I live in Canada, so I am entitled to maternity leave but I'm not sure if I will still be eligible if I change jobs this far in my pregnancy.

If anyone has any advice, I would really appreciate it. Thank you for taking the time to read this.