What would you do? Keep testing or not?

I have had an irregular cycle since my daughter was born two years ago. My last period started on Dec 10th, it was completely normal. I have yet to have a period again, I had very light brown mucus like spotting (I know TMI) on Jan 8th and 9th and then light cramps all day Jan 10th, I have taken several hpt's but negative. I don't know if it would be too early uming that if I was pregnant implantation occurred on Jan 10th. With my daughter I had the same thing (light cramps w/o period) and I took an hpt 5 days later and got a positive, but my cycle was really regular then. I just don't know if I should keep taking tests or not, my doctor told me to retest in 5 days, but I think that's like the standard answer anytime someone thinks they are pregnant and gets a negative. Me and my husband are trying to conceive again, but my heartaches every time a get a negative