IUD fail????

So, in September I chose to get the Skyla IUD because A) it regulated periods and I'd still get mine (supposedly) and B) it wasn't something I'd have to keep taking like a pill. The skyla has the lowest amount of hormones (I couldn't get a nonhormonal IUD because it causes a lot of bleeding and I'm anemic), and the skyla is also the smallest IUD. IUDs also have a 99.9% success rate, which sounded great to me because I'm only 17 and I had a baby in April, so I really needed something that would work but be low maintenance. So, I thought this was the perfect method for me.

The IUD didn't hurt getting put in, it was a small cramp and then the next two days I had period like cramping, and that was it! At the end of September I got my period, it wasn't too heavy or too light, and it lasted 6 days like my periods did before pregnancy, so at this point I was pretty pleased.

However, mid October I got a UTI and I didn't get my medicine for it until weeks later because my insurance was messing up. But, I was having sex during that time. Then, when I started my antibiotics (this was a week and a half ago) I was still having sex. (I just learned yesterday that antibiotics can make your birth control not work, so this is why I'm really worried).

Then, for the past 3 days I haven't felt right. I've been feeling nauseous everyday at the same times, getting horrible headaches, feeling bloated, and.... I didn't get my period in October and so far no period in November. Not even spotting.

So I'm not sure if what I'm feeling could be pregnancy symptoms or what.. I took a test but it was late in the afternoon after I downed some water. But, that test was negative. But I'm still feeling nauseous! I don't know what is going on and I don't know if it's IUD, UTI, or antibiotic related all I want to know is what can I do? Should I wait another week and wait for my period and take another test??? HELP