My last period was April 16, I had unprotected sex with my boyfriend on April 25 and 26. Its my second time to have sex but he used withdrawal method. 2 days after unprotected sex I feel tired, I had stomach cramps, nausea and my nipples hurt when touched. I had that feelings for 4 days. After that, my nipples doesn't hurt anymore when touched, but nausea is still there and sometimes stomach cramps and I think that I am bloated and I don't like to eat much but my stomach stings if I'd be late on my meals. It's been 16 days since my last sex, and I missed my period for 3 days. Are my signs/symptoms could be that I am pregnant? Please answer.

If you have sex, you can get pregnant. Symptoms mean almost nothing. Withdrawal has a terrible record for preventing conception. Your last period means little, too, because ovulation dates can vary from the usual 'mid-month' to any time.
Therefore, all you can do is wait until a HPT test kit will work, 2 weeks after the usual day your period was due. Meanwhile, please consider the pill or patch.
Is there any chance that your bf could have given you a STD? Perhaps both of you could be tested together, just for your peace of mind.

Of course you could be pregnant, that's what the sex act is about, REPRODUCING. Unfortunately after the deed is done you won't know for sure for quite some time if you are pregnant or not, no matter what symptoms you have.

Anything can throw a females cycle off, so relax and get some much needed education about your own body, and stop the irresponsible practice of unprotected sex. Worrying about being pregnant is useless after having unprotected sex, since you should have taken steps before you do the deed. No matter what form of birth control you use, or how many you use, there is still a chance of getting pregnant, and everyone should KNOW that.

Waiting is very hard so use the time to get facts before you get all freaked out about the unknown and PLEASE, talk to your boyfriend about your concerns and fears so he can LEARN to be a lot more responsible about this very natural instinct to make babies. You have no choice but to wait and see what happens NEXT.

The withdrawal method is the very worse method of birth control in the history of man, and you both could find out the facts about birth control before your feelings and fears run you nuts!

Any time there is penile insertion there is the risk of pregnancy. You can minimize the risk (and the "withdrawal method" is the least effective way) but not eliminate it. So yes you could be pregnant. But the first physical manifestation of pregnancy is a missed period. If your LMP was 4/16, it's a bit early to be sure you missed. Wait at least a week, preferably two. Then you can take a HPT.

As a norm, three days is not really considered late, since many women vary by a few days many months (a few will even miss a period now and then) Issues of diet, changes in routine, stress, worry and other issues can cause delays in cycle also.

Also withdrawal does not work well, it merely lowers the amount of sperm, it is very possible (easy) to get pregnant using that method.

Also two days after sex, the sperm may not have even implanted with the egg yet, it can take up to three days. (2 to 3 days)

You could be pregnant, but reporting symptoms "2 days" after sex is far too early. That may have actually been ovulation. That still poses an increased risk of pregnancy since sperm can live inside a woman for up to 2-3 days.

That said, your risk is high since you didn't use birth control. (Withdrawl is NOT a method, that's something ignorant horny people say to justify their actions)

Wait at least 4-5 more days, then test using first morning urine and by following the directions very carefully.