Tampons and not sure if pregnant?

I have been without a period since August. Last period started on the 10th and I spotted from then to the 28th of August. I finally on October 20th started what I thought was a period. It was so light which was odd for me. It was pretty much spotting for 2 1/2 days. Last week of September I had a lot of signs of pregnancy. Went to next pant size cause they were too tight and now the bigger ones are snug in my waist/stomach area. My tests are coming back negative. My thing is I have never had severe pain from using a tampon and I did the fiirst day using them. I was having bad pains in stomach and took the first one out and pain went away. I then put another one in and same thing a while later, crippling pain. I didn't have signs of the Toxic shock syndrome. I didn't use them for the remainder of the spotting which would of been usually a heavier period. I had a slight period before finding out I was pregnant with 4th child. If this is the case what would the effects be from using one? Any ideas would be helpful:0