I used to be a pushover in negotiations too. That's how I ended up making $55k when I later found out my coworkers were making $80k. So I applied and interviewed just to get practice with salary negotiating. After a week of trying I got an offer for $60k and I asked for $80 and we settled on $70. A week after being disappointed that I was making $55k while my coworkers made $80, I had a $15k increase. 3 months after that I switched companies and got another $10k increase. A year after that I switched companies again and got another $30k increase. Through negotiation, I doubled my salary from $55k to $110k in 15 months. It was uncomfortable at times, especially with counter offers and threatening to quit, but it's just business, and the other side of the table isn't losing any sleep over trying to lowball you.