your partner could have hsv1 orally whether he gets obvious cold sores to know it or not. You can contract herpes at any point in a relationship, it's not something you are necessarily going to contract within the first few weeks or anything.
If you are concerned, see your provider.
Can it be something else? b/c I haven't kissed anyone other than my partner of 4 yrs not even friendly cheek kisses w/ friends.
Oral herpes isn't an STD - it's transmitted via kissing, with many of us getting it in childhood from that big smooch from Auntie. More than 1/2 the adult population has oral herpes.
If you want to confirm that it is or isn't herpes, you'd need to be seen for a swab/culture of symptoms within the first couple days. Otherwise, you can get an IgG type specific blood test (as can your partner so you both know your herpes status).
You can read more about this incredibly common condition, here:
http://www.ashastd.org/herpes/herpes_learn_oralherpes.cfm