Is it an ulcer?

Ulcers can occur almost anywhere in the body, but I assume you are talking about gastric or peptic ulcers so we will proceed from there. A peptic ulcer is erosion in the lining of the stomach or duodenum (the first part of the small intestine). If a peptic ulcer is located in the stomach it is called a gastric ulcer.

Abdominal pain is a common symptom but it may not always be present. The abdominal pain from peptic ulcers can differ a lot from person to person. For example, the pain may get better or worse after eating a meal.

Nausea, vomiting
Weight loss
Fatigue
Heartburn, indigestion, belching
Chest pain
Vomiting blood
Bloody or dark tarry stools
Headache (due to blood loss or dehydration) - vomiting of blood or tarry stools would be present

However, these symptoms can also be indicative of other conditions. The symptoms you discribed could be from pregnancy, hormonal changes, change in diet, even some cancers.
You should consult your primary care physician who can arrange tests to determine more accurately what is going on. Best of luck to you. Susu