Pregnant or paranoid?

Okay so I started what I thought was my period on Sunday and I was supposed to get an IUD put in yesterday and my doctor wouldn't do it because she said my flow was not heavy enough and she wanted a blood pregnancy test to confirm. I took a first response and it was obviously negative. But I'm still worried the last time I had intercorse was the 27th, glow said I had a 3% chance of pregnancy we used the Trojan comdoms made with spermicide in it and check the condom afterwards and it didn't break. I have a highly stressful job and I'm planning a wedding. This situation is stressing me out even more! I guess my next step is to get the blood test but can so much stress make your period lighter?