How Is Mononucleosis Diagnosed?

Question: Can you have a low grade fever with mono and is there a blood test to
confirm it? Both my husband and I have, fever, chills, hot & cold, nausea, stomach pain that worsens after eating, sore throat, fatigue, weakness and lightheadedness. He had severe paint under his breastbone, along with nausea, but never threw up. We also both started out with constipation and then went to loose bowels and then diahrrea. He was hospitalized thinking he had an ulcer and so did they but unfortunately since he was also a heart patient (10 heart attacks, open heart surgery, stents, etc.) they concentrated on his heart instead of what we had come in for which was horrible stomach pain (which by the way he said it was almost as bad as having his heart attack). Needless to say, he was admitted and released a day later with no explanation and his heart was fine (which we knew). I, on the other hand, have everything he did except for the extreme pain under the breastbone, which now that I've read up on mono, I'm wondering if it may be his spleen enlarged. He is much better now, but still not well. I, however, have all these symptoms but mostly the nausea and feeling like someone punched me in the stomach as it worsens thru the day and after I eat. Saw the doctor late this afternoon and he is also stumped because we all thought that my husband had an ulcer (which he is getting tested for next week) but now since I have the same thing, he's really not sure and sent me home with getting a prescription for stomach relief that's called phen something. He says for now he'll just call it a virus. Do you have any ideas of what this could be? This has been going on for weeks.

Thank you so much for your answer which sounds right to me. However, I did want to add a few more symptoms which I forgot to tell you but may make no
difference in your diagnosis.

Although I said we had a fever and chills, this is on and off as it is low-grade and we'll get hot and then cold with chills, also on and off. The other symptom is that we both get extremely tired and have to lay down for a few hours to take a nap and it just seems to come on suddenly. I was driving home yesterday, about a 25 min. drive from my moms in the afternoon, and it was all I could do to keep my eyes open! Fortunately the other times this has happened, I was already at the house and could lay down.

As for the omeprazole, we both take it daily as it's one of our daily meds and has been for a year.

Neither one of us, though, has swollen lymphs but we do get a mild headache at times. We also both have lost 10 pounds in the last 2-3 weeks.

Is this contagious?