If you are outside with your Pom and a male dog approaches, it is best to pick up your Pomeranian and bring her back inside.
For exercise and play time outside, it is recommended to do this in a safe, enclosed environment such as a fenced in back yard. And if outside of that area, of course please keep your Pom on harness and leash.
This is not terribly uncommon and if it is to happen, it usually occurs with very young females or with senior Poms. When this occurs, the dog will appear to be entering her heat cycle...but it will only last for a few days (4 or 5 days). It will then stop and in 3 to 4 weeks she will enter a full heat. In most cases, conception cannot take place during the short phase of this.
For most Poms, having a split heat 1 or 2 times does not call out for medical intervention. However, if this happens frequently, the dog should have a complete checkup to rule out hypothyroidism or other possible underlying medical conditions.