As you yourself stated, canker sores are very common even in those who are celibate. They are not signs of any STD from vaginal intercourse. Bacterial vaginosis is also very common.
If you remain concerned, then get tested. Bacterial based testing for STD's such as chlamydia and gonorrhea check for the presence of the actual agent so testing for these can be done soon after the last sexual encounter.
Testing for viral based STD's such as HIV, and herpes, etc. check for antibodies the immune system begins to produce after transmission has taken place. For these the recommended time period for testing is 3 months after the last possible exposure.
Promise yourself that from now on, you will not engage in unprotected sexual intercourse (i.e., intercourse without a condom) unless you have actual proof that your partner is STD free. That way you can worry a whole lot less about all of this.
Most folks who carry this virus (and yes, the majority of adults have this, having picked this up in childhood), rarely or never have an outbreak. Children often pick this up because they have a tendency to "mouth" everything, toys, keys, etc..
It's likely the person you've gained feelings for may also carry this virus then. This is really a very common virus.