I delivered my son 2 months 1 week ago. Fully breastfeeding with break no more than 6 hrs overnight and feeding 2-4hrly during day. For 4 days I have had mild period like pain without bleeding. Initially 2 days in a row had I spot of blood, and have slight clear discharge no foul odor. My husband and I are using withdrawal method only. I'm hoping this can be normal?? I hope it doesn't mean I am getting implantation bleeding this soon?

It can be normal, since exclusive breastfeeding, combined with withdrawal (even though it is not the most reliable means) will decrease the odds significantly.
However, it is also possible it can be due to pregnancy. Plenty of women are surprised to find themselves pregnant again soon after the birth of a child.

While breastfeeding you may find you have occasional spotting or you may start up your periods before long. The drop in a night feed may be enough for your body to get things going again.

Remember, you ovulate before a period, so it would be a good idea to use an additional form of birth control now that your son is giving you a nice six hour stretch at night.

Give it another week, and try a pregnancy test. If negative, discuss with your doctor other birth control options. If you can use hormonal ones, the mini-pill can be a good option while breastfeeding.